https://wise.com/help/articles/29779...unts-with-wise
This says "Wise is regulated by the FCA in the UK " but I don't know what that means but pretty sure it doesn't automatically mean that you are covered by the FSCS up to £85,000.
If they're offering an interest bearing account then the value of your underlying $ shouldn't be at risk as it would be if they were investing in equities, etc..
EDIT: Not sure this clariies:
https://wise.com/help/articles/2736047/do-i-earn-interest-on-my-balances-or-jars?origin=search-interest