Just this week we addressed some accessibility issues (also including missing labels and such) on Vivaldi on Android and hope to do the same on desktop (no ETA unfortunately).
It would help us a lot, if you could file a bug report on https://vivaldi.com/bugreport/ with issues that are especially annoying for you, so we could prioritize those.
If you do, please share the bug number(s) you receive in an email, so I can follow up. Thank you!