Guys,
a quick thank you. Especially to
@CaseySJ. I today came here to check for the steps necessary updating from 11.3 to 11.6. Was about time securitywise. Updated OC with a fully automated tool (HackinDrom), did the bootable backup with a fully automated script, updated BIG Sur via System Updates. Read everything about it in various meticulously compiled guides. Flawless.
Man, I am running this machine since early 2019 and while it was some fiddling back then starting with mojave and buggy gfx drivers it‘s so smooth and easy meanwhile. Thanks to everyone contributing here.