It's gone up in recent years
https://www.instituteforgovernment.org.uk/explainers/welsh-independence
Between one quarter and one third
https://nation.cymru/news/poll-shows-highest-support-for-welsh-independence-ever-recorded/
This poll had it at 39%
It really depends who/where you ask.
I think with creative sqmple selection you could get pretty much whatever you wanted out of Wales for that