Cannot get custom kernel to boot - mkinitpcio does not add any modules

1. What I am trying to achieve:

• Build a custom kernel so I can install and run Anbox-git from AUR on my Arch laptop. Custom kernel is needed for the package to work.

2. What I did to achieve it:

• Download Arch Linux kernel v5.8.5-arch1 from here
• I followed the guidelines on tradional compilation Arch wiki to create the custom kernel
• Via make nconfig I applied the changes mentioned in the Anbox Arch wiki page.
• Via make nconfig I changed EFIVAR_FS option from "M" to "*" to resolve an error from earlier attemps.
• Via make nconfig under Location: -> Device Drivers-> Multiple devices driver support (RAID and LVM) (MD [=y])-> Device mapper support (BLK_DEV_DM [=y]) I added a few more options (*) because on earlier builds mkinitpcio gave errors for missing modules for DM_CRYPT, and some more DM_ modules which I cannot easily reproduce (will do if necessary for the answer, but I hope it'll be irrelevant).

After creating the config this way I did:

• sudo make modules_install
• sudo cp -v arch/x86_64/boot/bzImage /boot/vmlinuz-linux58ac
• sudo cp /etc/mkinitcpio.d/linux.preset /etc/mkinitcpio.d/linux58ac.preset
• Adapted the preset file per Arch wiki instructions
• sudo mkinitcpio -p linux58ac

Important: The mkinitpcio runs fine, but keeps giving me a warning:

WARNING: No modules were added to the image. This is probably not what you want.

• sudo grub-mkconfig -o /boot/grub/grub.cfg

3. Expected result:

I am able to reboot, select the new kernel from grub menu, get the usual LVM password prompt, and launch into it without problems.

4. Result I get:

I can reboot and select new kernel from grub but when I select it I get a

Warning: /lib/modules/5.8.5-arch1/modules.devname not found, ignoring.
Starting version 246.4-1-arch
ERROR device 'dev/mapper/vg0-root' not found. Skipping fsck. 
mount /new_root: special device /dev/mapper/vg0-root does not exist.
You are being dropped into an emergy shell. 

I checked and the /lib/modules/5.8.5-arch1/modules.devnamedoes indeed exist. But I think the actual problem is that mkinitcpio doesn't load the correct modules into the custom kernel, causing it to become unbootable.

Any help appreciated!