Yeah you can use the original bootloader with this kernel, if you copy manjaros cmdline.txt file, and then rename the Image to kernel8.img like manjaro uses, then you will need an initramfs file. If you install this kernel I will link you, you could use those files and just rename the Image to Kernel8.img (I think that is what manjaro uses, you'd have to verify in the cmdline.txt. Then you would need to copy the overlays folder and it would be used in place of the dtbs folder, but to be proper they would need to be build against the 5.8.10 kernel which is not currently done since i am using the uboot method still. I found it to be fine once USB is working. Make a backup of your /boot to somewhere you will remember, and somewhere you can access if the Pi is un-bootable for whatever reason. This kernel WILL replace the linux-aarch64, so you would need to uninstall my kernel and reinstall the linux-aarch64 package if you want to use the arch provided mainline kernel. I only use my pi headless with no gui, so you'll have to let me know if there is any issues. I may have to add the modules in for sound again. If you're up for trying it, and it solves your issues we can make sure it will work for you, or you can copy the config while you are booted on the kernel with zcat /proc/config.gz > kernelconfig, and modify it to build your own kernel. I cross compile my kernels and the Pi runs the repository for my other computers. Give it a shot, and let me know if it is working. If you are only using an SD card, you can just cd into your boot directory after install the kernel (before rebooting) and run ./mkscr to generate the uboot image. If you are using a different device rather than the second partition on your SD card, you will need to change the boot.txt file to your root drive. I point to mine with the UUID. As long as you make a backup, you will be able to restore what you have now if things don't workout how you'd like. I put them on dropbox for now for anyone that would like to try them. If you end up liking it, we can set you up so you can just use pacman to update the kernel. I usually build them on thursdays when the kernels typically are updated. Surely you know, but after you download them, use pacman -U *.pkg.tar.xz to install all three of them, or you can do them individually, your choice.
https://www.dropbox.com/s/zwc236qdun21o ... ar.gz?dl=0