Not downloading updates


New Member
I'm on a new computer which arrived 3 days ago. When I first loaded it Windows Update downloaded and installed a couple of updates without problem, but now it's stuck.
I had 3 outstanding updates: 2021-01 KB4589212 and 2021-03 KB5000802, plus Feature Update to Windows 10 version 20H2 which has its own Download and Install, I tried to install 20H2. The next morning it had an error "We couldn't install this update, but you can try again (0x80244018)".
Restarted computer, checked update, it shows the same 3 Updates 2021-01 KB4589212 and 2021-03 KB5000802, plus of course Feature Update.
Ran Windows Update troubleshooter, it said "service registration is missing or corrupt.....fixed" but nothing changes.
Both the 2021 updates show Downloading 0%, even after hours of waiting.
I use Norton 360, I've tried disabling the firewall but nothing changes.
I see various "solutions" online, some suggest BITS should be automatic, others say manual, I've tried both to no effect. If I set it to auto it eventually returns to manual.
I have no idea what to do now.
Windows update problems have been happening for over 30 years in goodness knows how many different flavours of Windows. To my simple mind it's only a question of download a few files, copy them to the right place, restart, rinse and repeat. Why Microsoft can't make this process bullet-proof is beyond me but it's darned annoying.
Does anyone have any idea how to fix this?

Many thanks