More than year absence in the UK


Even though I couldn’t find official guidance on this, as far as I understand, after getting the visa (which will be 5 years in my case) one can move out to another country for years having the GTV visa valid throughout the whole initial duration.
However, won’t it negatively affect the extension decision even if one moves to the UK a year before the expiration and starts working in tech?
I am also from a country citizens of which should register in the police (Registering as an overseas visitor - OVRO). Should I register my absence in the UK? Also how to register it if I don’t know the date of return to the UK?

Thank you in advance!

P.S. I am aware that the years when one spends less than 180 days in the UK don’t count towards ILR and that is why I am interested in a potential extension.