@Shantur I confirm your results trying to boot that kernel image in QEMU and unfortunately there does not appear to be a debug symbols package generated so I cannot debug it.

I should do more thorough checks first! I had accidentally fetched the amd64 kernel image!! *red faced*

So, this build DOES boot successfully with long parameters with QEMU:

$ qemu-system-aarch64 -machine virt,gic-version=3 -cpu max,pauth-impdef=on -smp 2 -m 4096 -nographic -kernel ./vmlinuz-6.8.0-39
-generic -append "debug $( for l in {144..157}; do echo -n param$l=$(pwgen $((l-9)) 1)' '; done )" -initrd rootfs/boot/initrd.img-6.8.12-arm64-debug
[    0.000000] Booting Linux on physical CPU 0x0000000000 [0x000f0510]
[    0.000000] Linux version 6.8.0-39-generic (buildd@bos03-arm64-061) (aarch64-linux-gnu-gcc-13 (Ubuntu 13.2.0-23ubuntu4) 13.2.0, GNU ld (GNU Binutils
for Ubuntu) 2.42) #39+TEST2069534v20240727b1-Ubuntu SMP PREEMPT_DYNAMIC Sat Jul 27 (Ubuntu 6.8.0-39.39+TEST2069534v20240727b1-generic 6.8.8)
[    0.000000] KASLR enabled
[    0.000000] random: crng init done
[    0.000000] Machine model: linux,dummy-virt
...
[    0.000000] Kernel command line: debug param144=voorainu7ohRiewieTh4mahk6thoh5tahheex0aewei5ohCahHa8eefae1Iuw1tei3aethu1aen6Aewoi6omoox0iexiebafieShaidohraozaigi4ohng1iLai4eeniz4Eh0ah param145=eesh4eequaequ2coovie2goa0fohZah3ahToop0Aihail7feeVohgaepi9EiGae7oongoo6queihoh3ukeinahh4io5peikae5iidohqueGh6Er0CaeP6kaWaezothahK2uX1af7 param146=ui2phaej7cho6Daip3ahhoze9noQuie1uzaiquaer9aPhae1TiShaekae7Cooj6an3be4aiQuae2euz7aehueQuoo1eThi9jahc1Ahsuraequ0Al4L
ietheeleso5ji6reich2hai param147=OoRohkei8eex5thair8KeeCh5kea1miepheigh2phahsiqueethoo0eequahs6Fiecoo6HeuQuohte7ooxipoo0seethai9quo7ogoo1caibeiphoh0ahth
8heiPo8nucohg5shewo param148=sheim7muoCaingiegeepeimuokooghab4oXouX3ge8leeN3Roog9eeMah8ahb5iuxaifaig5ahPoh1pa9Aebeech2go5JooN8xawah5ohLi7thee8lei5aiX6oh
kae4giexohcagee2 param149=ojae4cho8eec2kithu6aelai0ieshai6iepeiY7aiTh8Oophub5ahdouWaiguuY6deidecooShaiziew2fiegeCuukooz3AiCiVaid4shaaceixochejoozaiSaiYa
ipeiJ9eelechuj param150=Eipee9ohb7ifohcato7paisho9een3tiev7eexah2iephaey0zah0zahjeeV6Ca7theiPeapae5eengaeshoothaibooS7aesoo9
...
[    3.083720] Run /init as init process
[    3.084590]   with arguments:
[    3.085474]     /init
[    3.085815]   with environment:
[    3.086312]     HOME=/
[    3.086631]     TERM=linux
[    3.086959]     param144=voorainu7ohRiewieTh4mahk6thoh5tahheex0aewei5ohCahHa8eefae1Iuw1tei3aethu1aen6Aewoi6omoox0iexiebafieShaidohraozaigi4ohng1iLai4
eeniz4Eh0ah
[    3.088406]     param145=eesh4eequaequ2coovie2goa0fohZah3ahToop0Aihail7feeVohgaepi9EiGae7oongoo6queihoh3ukeinahh4io5peikae5iidohqueGh6Er0CaeP6kaWaezo
thahK2uX1af7
[    3.089842]     param146=ui2phaej7cho6Daip3ahhoze9noQuie1uzaiquaer9aPhae1TiShaekae7Cooj6an3be4aiQuae2euz7aehueQuoo1eThi9jahc1Ahsuraequ0Al4Lietheeleso
5ji6reich2hai
[    3.091349]     param147=OoRohkei8eex5thair8KeeCh5kea1miepheigh2phahsiqueethoo0eequahs6Fiecoo6HeuQuohte7ooxipoo0seethai9quo7ogoo1caibeiphoh0ahth8heiP
o8nucohg5shewo
[    3.092792]     param148=sheim7muoCaingiegeepeimuokooghab4oXouX3ge8leeN3Roog9eeMah8ahb5iuxaifaig5ahPoh1pa9Aebeech2go5JooN8xawah5ohLi7thee8lei5aiX6ohk
ae4giexohcagee2
[    3.094310]     param149=ojae4cho8eec2kithu6aelai0ieshai6iepeiY7aiTh8Oophub5ahdouWaiguuY6deidecooShaiziew2fiegeCuukooz3AiCiVaid4shaaceixochejoozaiSai
YaipeiJ9eelechuj
[    3.095763]     param150=Eipee9ohb7ifohcato7paisho9een3tiev7eexah2iephaey0zah0zahjeeV6Ca7theiPeapae5eengaeshoothaibooS7aesoo9keeyolaeWuaGhuGai5paxia2
OPhiilohnohk4ceed
[    3.097292]     param151=eich9ooDeiMeengahsah4thahbohngaoK1eX2Eh2gaiGu9jiquohKoC8toh0vat0noQueep6Eiw8aiyaCaeTh1OosahghiQua8siefaegi6SaidohphieS2ohgh1
ia3aeFeo1ahgeiface
[    3.098808]     param152=Xoxohr4riebo6coo7aicheetaeceez0chei7ohyaeJusah9uN1yu4thahzi4xoh6OhW2Meish6aeDeicoh7EeCh4eXahd0iekaiQuee0niesei6eiy7aoG0sooyo
2itaP2af5ahk6joh4to
[    3.100321]     param153=ha7naihiXiew4Meegah3coo5eeb0foo1AezeeXoo6shu8eimaiVaekeeTh6thirookeeN4woozapaitah8aeHai8aefoh9ae0Augoo1ahQu4ohchee0neix5vo9a
esoo7ohN7ei1Eivahwev
[    3.101823]     param154=yu9Iu4eiGe6gaishiateeng4Aiwaer9Chai8fai9miesieb3co1De6koow2iebahV6AhguGiechooseb8Mu0peish9ahaweiS1beig1oochiefi3Uu6chongae2p
hoch6pee5daa3quee3eiz
[    3.103344]     param155=athu5ohzei5aivaexai1ahKoquaijusinoolohx5shuomuovaewahmaWoh6quoh2aifeethoph5ohyiiy9coo2ge4meiNgieChoo5eixiech3aeziel6giejeizu
agh9ieveibiHijaid4oo3e
[    3.104858]     param156=yeech7uv7eedie6Wie0zooDiey7ahkoJ0wai8su1yooPhahHohuwi5rahsheequoomiom5atiegh9ahPhiem3mol0soothaotheifah1ohfi8theek2ajohx6Aeg
h0eera2seishiesieb2cae8
[    3.106394]     param157=shoo9hei9ohLix2ed6HeeVohx3ieZahm7Oa7choo3rieshae4beiyei3AiGhi9ue5oyoo
...
BusyBox v1.35.0 (Debian 1:1.35.0-4+b3) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs) uname -a
Linux (none) 6.8.0-39-generic #39+TEST2069534v20240727b1-Ubuntu SMP PREEMPT_DYNAMIC Sat Jul 27 aarch64 GNU/Linux
(initramfs) cat /proc/cmdline | wc -c
2048
(initramfs) cat /proc/cmdline
debug param144=voorainu7ohRiewieTh4mahk6thoh5tahheex0aewei5ohCahHa8eefae1Iuw1tei3aethu1aen6Aewoi6omoox0iexiebafieShaidohraozaigi4ohng1iLai4eeniz4Eh0ah p
aram145=eesh4eequaequ2coovie2goa0fohZah3ahToop0Aihail7feeVohgaepi9EiGae7oongoo6queihoh3ukeinahh4io5peikae5iidohqueGh6Er0CaeP6kaWaezothahK2uX1af7 param14
6=ui2phaej7cho6Daip3ahhoze9noQuie1uzaiquaer9aPhae1TiShaekae7Cooj6an3be4aiQuae2euz7aehueQuoo1eThi9jahc1Ahsuraequ0Al4Lietheeleso5ji6reich2hai param147=OoR
ohkei8eex5thair8KeeCh5kea1miepheigh2phahsiqueethoo0eequahs6Fiecoo6HeuQuohte7ooxipoo0seethai9quo7ogoo1caibeiphoh0ahth8heiPo8nucohg5shewo param148=sheim7m
uoCaingiegeepeimuokooghab4oXouX3ge8leeN3Roog9eeMah8ahb5iuxaifaig5ahPoh1pa9Aebeech2go5JooN8xawah5ohLi7thee8lei5aiX6ohkae4giexohcagee2 param149=ojae4cho8e
ec2kithu6aelai0ieshai6iepeiY7aiTh8Oophub5ahdouWaiguuY6deidecooShaiziew2fiegeCuukooz3AiCiVaid4shaaceixochejoozaiSaiYaipeiJ9eelechuj param150=Eipee9ohb7if
ohcato7paisho9een3tiev7eexah2iephaey0zah0zahjeeV6Ca7theiPeapae5eengaeshoothaibooS7aesoo9keeyolaeWuaGhuGai5paxia2OPhiilohnohk4ceed param151=eich9ooDeiMee
ngahsah4thahbohngaoK1eX2Eh2gaiGu9jiquohKoC8toh0vat0noQueep6Eiw8aiyaCaeTh1OosahghiQua8siefaegi6SaidohphieS2ohgh1ia3aeFeo1ahgeiface param152=Xoxohr4riebo6
coo7aicheetaeceez0chei7ohyaeJusah9uN1yu4thahzi4xoh6OhW2Meish6aeDeicoh7EeCh4eXahd0iekaiQuee0niesei6eiy7aoG0sooyo2itaP2af5ahk6joh4to param153=ha7naihiXiew
4Meegah3coo5eeb0foo1AezeeXoo6shu8eimaiVaekeeTh6thirookeeN4woozapaitah8aeHai8aefoh9ae0Augoo1ahQu4ohchee0neix5vo9aesoo7ohN7ei1Eivahwev param154=yu9Iu4eiGe
6gaishiateeng4Aiwaer9Chai8fai9miesieb3co1De6koow2iebahV6AhguGiechooseb8Mu0peish9ahaweiS1beig1oochiefi3Uu6chongae2phoch6pee5daa3quee3eiz param155=athu5oh
zei5aivaexai1ahKoquaijusinoolohx5shuomuovaewahmaWoh6quoh2aifeethoph5ohyiiy9coo2ge4meiNgieChoo5eixiech3aeziel6giejeizuagh9ieveibiHijaid4oo3e param156=yee
ch7uv7eedie6Wie0zooDiey7ahkoJ0wai8su1yooPhahHohuwi5rahsheequoomiom5atiegh9ahPhiem3mol0soothaotheifah1ohfi8theek2ajohx6Aegh0eera2seishiesieb2cae8 param15
7=shoo9hei9ohLix2ed6HeeVohx3ieZahm7Oa7choo3rieshae4beiyei3AiGhi9ue5oyoo