UPDATE:
Managed to make it work but not sure if in the right conditions.
After rummaging a lot of sites looking for GPU related issues I got enough info to launch Vivaldi via CLI with some flags. None of the suggested worked (maybe because the problem was different) but when I tried:
/usr/bin/vivaldi-stable --disable-gpu
the browser started normally. 😮
After that I went to Vivaldi settings and disable the hardware acceleration option
I'll stick with Firefox for now but let's see if future updates will make it work without disabling hardware