I got the files for the kernel and did this (many warnings, one error):

(base) david:new-kernel$ sudo dpkg -i *.deb
Selecting previously unselected package linux-headers-5.8.0-050800.
(Reading database ... 454198 files and directories currently installed.)
Preparing to unpack linux-headers-5.8.0-050800_5.8.0-050800.202007052030_all.deb ...
Unpacking linux-headers-5.8.0-050800 (5.8.0-050800.202007052030) ...
Preparing to unpack linux-headers-5.8.0-050800-generic_5.8.0-050800.202007052030_amd64.deb ...
Unpacking linux-headers-5.8.0-050800-generic (5.8.0-050800.202007052030) over (5.8.0-050800.202007052030) ...
Preparing to unpack linux-image-unsigned-5.8.0-050800-generic_5.8.0-050800.202007052030_amd64.deb ...
Unpacking linux-image-unsigned-5.8.0-050800-generic (5.8.0-050800.202007052030) over (5.8.0-050800.202007052030) ...
Selecting previously unselected package linux-modules-5.8.0-050800-generic.
Preparing to unpack linux-modules-5.8.0-050800-generic_5.8.0-050800.202007052030_amd64.deb ...
Unpacking linux-modules-5.8.0-050800-generic (5.8.0-050800.202007052030) ...
Setting up linux-headers-5.8.0-050800 (5.8.0-050800.202007052030) ...
Setting up linux-headers-5.8.0-050800-generic (5.8.0-050800.202007052030) ...
Setting up linux-modules-5.8.0-050800-generic (5.8.0-050800.202007052030) ...
Setting up linux-image-unsigned-5.8.0-050800-generic (5.8.0-050800.202007052030) ...
Processing triggers for linux-image-unsigned-5.8.0-050800-generic (5.8.0-050800.202007052030) ...
/etc/kernel/postinst.d/initramfs-tools:
update-initramfs: Generating /boot/initrd.img-5.8.0-050800-generic
modinfo: ERROR: could not get modinfo from 'da903x': No such file or directory
W: Possible missing firmware /lib/firmware/amdgpu/navi12_gpu_info.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_gpu_info.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_ta.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_asd.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_sos.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_ta.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_asd.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_sos.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi14_ta.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/vega20_ta.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_rlc.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_mec2.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_mec.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_rlc.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_mec2.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_mec.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_me.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_pfp.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_ce.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_sdma.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_sdma1.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_sdma.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi10_mes.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_vcn.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_vcn.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_smc.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/arcturus_smc.bin for module amdgpu
W: Possible missing firmware /lib/firmware/amdgpu/navi12_dmcu.bin for module amdgpu
/etc/kernel/postinst.d/zz-update-grub:
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/init-select.cfg'
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.8.0-050800-generic
Found initrd image: /boot/initrd.img-5.8.0-050800-generic
Found linux image: /boot/vmlinuz-5.4.0-40-generic
Found initrd image: /boot/initrd.img-5.4.0-40-generic
Found linux image: /boot/vmlinuz-5.4.0-39-generic
Found initrd image: /boot/initrd.img-5.4.0-39-generic
Found linux image: /boot/vmlinuz-4.15.0-101-generic
Found initrd image: /boot/initrd.img-4.15.0-101-generic
Adding boot menu entry for UEFI Firmware Settings
done

I will edit grub.cfg and try this. Just saving here before I do.