Amiberry v5 (April 2022) with RetroPie 4.8
If you cant wait for Amiberry v5 on the Pi, here is how to manually install it on RetroPie 4.8. I'd recommend waiting for the official integration, but this lets you get up and running if you want to try it now.
UPDATE:
I fixed Historyline with the values here :)
https://github.com/Voljega/amiga4recalbox#startup-sequence-tweaking-for-experts-only
whdload_custom1=2
/opt/retropie/configs/amiga/amiberry/conf/Historyline_v1.5_1569.uae
Amiberry
https://blitterstudio.com/amiberry/
Amiberry Releases (v5)
https://github.com/midwan/amiberry/releases
"amiberry-v5.0-rpi4-dmx-32bit-retropie.zip"
Guide to manually update to v5
https://github.com/midwan/amiberry/wiki/Upgrading-to-the-latest-version
RetroPie Amiberry forum thread
https://retropie.org.uk/forum/topic/12656/amiga-amiberry-whdload-holy-grail-amiberry-s-official-thread
Amiberry Conf file options
https://github.com/midwan/amiberry/wiki/Amiberry.conf-options
Set the "CUSTOM1" style flags
https://github.com/midwan/amiberry/wiki/WHDLoad-Auto-booting