@zmaint I had a look inside. I cannot see the bios battery straight away, and I am a little scared to disassemble a brand new PC, even if it is only doing half of what I want it to do now. Thanks a lot for the idea - maybe someone braver than me browsing these fora will make use of it (or I will, when frustrated enough).
I looked into RHEL, but if I understand it correctly, it's really for companies only and the process asks for a fairly involved registration, together with the company name and stuff - not for me, even to play around with - but I gave CentOS a go and though there is more information now, the end result did not change: https://ibb.co/P94t0hw
I took pictures of my bios settings, however: https://ibb.co/album/FkjN30