I don't use Ubuntu kernels; build my own mainline but work on kernel issues in mainline and Debian. I tested 144..157 length (interestingly although arm64 professes to support 2048 characters the kernel messages are truncated at around 1000 so don't show the entire thing).

$ qemu-system-aarch64 -machine virt,gic-version=3 -cpu max,pauth-impdef=on -smp 2 -m 4096 -nographic -kernel /srv/NAS/Sunny/SourceCode/builds/linux-aarch64/arch/arm64/boot/Image -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 6.8.12 (<email address hidden>) (aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40) #10 SMP Fri
Jul 26 13:57:53 BST 2024
[    0.000000] random: crng init done
[    0.000000] Machine model: linux,dummy-virt
...
[    0.000000] Kernel command line: debug param144=aixootoo9ii0dieghaem2eehahqu9Aejeuka3ui8chain9ief3Ooth9lahgeiyiew3dio3PhahpeiShoh1ootoch2rae9quushei9yu4ge5uasi9peizooT8JohjieMuGh7ohs7 param145=noohieL5DaeghaeGh4nueQuugoowohj6fa0Jaive7meaghukoog8tho6De6ahga7sheighah2Raing9eitai3eeHi4Ahr7aixaiLoh3cheeG
hosa9eR4sohkajahwe1tha9aotha param146=taesaekie3Vaiv2Neejohph0ozeile5daemu8beepha9Ojae8niev8nepaidaemu9uphaah4bongeiRahM5eichahTah6aegob8edee2xah6UaxahThee2puePua5ahchoqueixee param147=ahZai6EeW1EejaGh6hen6eu6oov6wo3ooph5theide6OhGh5oog2Iel8oong1ighooboo7ohthoh2le5eeloog1agha0phaid5enaeQuohfoo3EijaemeiZ
9ohG5aichoo9shuiFee param148=ieT6oogat5sheng9aeteigh4poohoongul5za7Eich5Abo2Aeraec0eingah5ahsh4Ooth9Phaithai3gethoo4piphie0zieHieYahngahbiitheingooshau4
chaepee2zeeWei5a param149=eenga3ku8deongie7Oovahsoo7ao1zail8remu2ieshai6haemee2eingoophev6eeY5KeeChiemeu2Eaquuqu8ahk3oohovoh6vaijaexoodeesoetuucie7geeba
h5cad5aikoh6mo param150=oopaiCh0thu1ioneed3apee9igieT7OaWedeemoop4izex9gaeRaequai6aavaephua4ahlooThaiquie4Gu8Eiyo8ohmai1aiye
...
[    3.045515] Run /init as init process
[    3.045717]   with arguments:
[    3.045852]     /init
[    3.045962]   with environment:
[    3.046098]     HOME=/
[    3.046206]     TERM=linux
[    3.046320]     param144=aixootoo9ii0dieghaem2eehahqu9Aejeuka3ui8chain9ief3Ooth9lahgeiyiew3dio3PhahpeiShoh1ootoch2rae9quushei9yu4ge5uasi9peizooT8Johj
ieMuGh7ohs7
[    3.046913]     param145=noohieL5DaeghaeGh4nueQuugoowohj6fa0Jaive7meaghukoog8tho6De6ahga7sheighah2Raing9eitai3eeHi4Ahr7aixaiLoh3cheeGhosa9eR4sohkajah
we1tha9aotha
[    3.047481]     param146=taesaekie3Vaiv2Neejohph0ozeile5daemu8beepha9Ojae8niev8nepaidaemu9uphaah4bongeiRahM5eichahTah6aegob8edee2xah6UaxahThee2puePua
5ahchoqueixee
[    3.047963]     param147=ahZai6EeW1EejaGh6hen6eu6oov6wo3ooph5theide6OhGh5oog2Iel8oong1ighooboo7ohthoh2le5eeloog1agha0phaid5enaeQuohfoo3EijaemeiZ9ohG5
aichoo9shuiFee
[    3.048466]     param148=ieT6oogat5sheng9aeteigh4poohoongul5za7Eich5Abo2Aeraec0eingah5ahsh4Ooth9Phaithai3gethoo4piphie0zieHieYahngahbiitheingooshau4c
haepee2zeeWei5a
[    3.048992]     param149=eenga3ku8deongie7Oovahsoo7ao1zail8remu2ieshai6haemee2eingoophev6eeY5KeeChiemeu2Eaquuqu8ahk3oohovoh6vaijaexoodeesoetuucie7gee
bah5cad5aikoh6mo
[    3.049508]     param150=oopaiCh0thu1ioneed3apee9igieT7OaWedeemoop4izex9gaeRaequai6aavaephua4ahlooThaiquie4Gu8Eiyo8ohmai1aiyeib9ahkaifeh3ahqu5joutugh
1hee7ShiePhieThai
[    3.050024]     param151=aiVeiT2Aw0EenaizeeKaezei8eigei2Luov0ohdeeng6miekooZuD9ieci3oph6pahs9upid6Aesou6uiboongei7aVie2ushai8iex3quahzieH5eingaengao2
OhsheiHoo4Hiehei6N
[    3.050564]     param152=eivohroQui8quoh5jeizoo1ook6toothahchei3Iethee6au6irae3quee8AhLae9FaceuZahsahqueig9iec1jae9fier9Ohmaengohpheing4eimaipah3pahs
h4uo1Eefauroong1hiz
[    3.051316]     param153=juh6ahbu2raena5uocejaqueeduyohB6uasiex5ahtaiTieK3Ruol1ceijin4quah3Fee7ahthaiphoo8piaghaegomeez3aichee4doreiloh6dieL5chae0oor
ahth1shoz7cheesarood
[    3.051860]     param154=ainaa7XahH8phoobeefaebaepaivee9kierohse7OopooshahphiengogahThood6qua3woh5aiziungae1sai6ao7phahW0Ooph6fahk0uph3wieghai1ootoh4
Oogei6Jaeboupheehepho
[    3.052373]     param155=zienga1nee1CaiFeiv7Kae8ohma2ceejeif3pung2zi2shoigohn6choh6Oon7iaxie1Kua2waFoophier0uaf9aivoh1cee9chooha1phughohx8Abei9de9lai
kuaz6pheeD3pohbeic7sah
[    3.052903]     param156=aiyahy5ieghoo5eenaipethei7chebi4thaek5iqu5eelah5au3Eishil5Aichae3guqueiPei2ahdeeghiteequeichooWah2othee1thee4Zohgo5deem9aigh
0eef2sha2wei0sed8aiquoo
[    3.053432]     param157=iiph5iewudai5SahbiY4holoos3nis2Caeheibav0eu9EijaebahzeBuathei7xohngah
...
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) cat /proc/cmdline
debug param144=aixootoo9ii0dieghaem2eehahqu9Aejeuka3ui8chain9ief3Ooth9lahgeiyiew3dio3PhahpeiShoh1ootoch2rae9quushei9yu4ge5uasi9peizooT8JohjieMuGh7ohs7 param145=noohieL5DaeghaeGh4nueQuugoowohj6fa0Jaive7meaghukoog8tho6De6ahga7sheighah2Raing9eitai3eeHi4Ahr7aixaiLoh3cheeGhosa9eR4sohkajahwe1tha9aotha param146=taesaekie3Vaiv2Neejohph0ozeile5daemu8beepha9Ojae8niev8nepaidaemu9uphaah4bongeiRahM5eichahTah6aegob8edee2xah6UaxahThee2puePua5ahchoqueixee param147=ahZai6EeW1EejaGh6hen6eu6oov6wo3ooph5theide6OhGh5oog2Iel8oong1ighooboo7ohthoh2le5eeloog1agha0phaid5enaeQuohfoo3EijaemeiZ9ohG5aichoo9shuiFee param148=ieT6oogat5sheng9aeteigh4poohoongul5za7Eich5Abo2Aeraec0eingah5ahsh4Ooth9Phaithai3gethoo4piphie0zieHieYahngahbiitheingooshau4chaepee2zeeWei5a param149=eenga3ku8deongie7Oovahsoo7ao1zail8remu2ieshai6haemee2eingoophev6eeY5KeeChiemeu2Eaquuqu8ahk3oohovoh6vaijaexoodeesoetuucie7geebah5cad5aikoh6mo param150=oopaiCh0thu1
ioneed3apee9igieT7OaWedeemoop4izex9gaeRaequai6aavaephua4ahlooThaiquie4Gu8Eiyo8ohmai1aiyeib9ahkaifeh3ahqu5joutugh1hee7ShiePhieThai param151=aiVeiT2Aw0EenaizeeKaezei8eigei2Luov0ohdeeng6miekooZuD9ieci3oph6pahs9upid6Aesou6uiboongei7aVie2ushai8iex3quahzieH5eingaengao2OhsheiHoo4Hiehei6N param152=eivohroQui8quoh5jeizoo1ook6toothahchei3Iethee6au6irae3quee8AhLae9FaceuZahsahqueig9iec1jae9fier9Ohmaengohpheing4eimaipah3pahsh4uo1Eefauroong1hiz param153=juh6ahbu2raena5uocejaqueeduyohB6uasiex5ahtaiTieK3Ruol1ceijin4quah3Fee7ahthaiphoo8piaghaegomeez3aichee4doreiloh6dieL5chae0oorahth1shoz7cheesarood param154=ainaa7XahH
8phoobeefaebaepaivee9kierohse7OopooshahphiengogahThood6qua3woh5aiziungae1sai6ao7phahW0Ooph6fahk0uph3wieghai1ootoh4Oogei6Jaeboupheehepho param155=zienga1
nee1CaiFeiv7Kae8ohma2ceejeif3pung2zi2shoigohn6choh6Oon7iaxie1Kua2waFoophier0uaf9aivoh1cee9chooha1phughohx8Abei9de9laikuaz6pheeD3pohbeic7sah param156=aiyahy5ieghoo5eenaipethei7chebi4thaek5iqu5eelah5au3Eishil5Aichae3guqueiPei2ahdeeghiteequeichooWah2othee1thee4Zohgo5deem9aigh0eef2sha2wei0sed8aiquoo param157=iiph5iewudai5SahbiY4holoos3nis2Caeheibav0eu9EijaebahzeBuathei7xohngah
(initramfs) cat /proc/cmdline | wc -c

2048