the default weather module still uses 2.5 and it works
at the moment, yes.
I looked into their api stuff and onecall v2.5 is not mentioned anymore. The normal endpoints weather and forecast are still on v2.5.
Problem: For onecall 3.0 you need a special api key (as already mentioned here) with a subsciption where you have to give your payment data (1000 request free per day, limit is 2000 per day but you can set your limit to 1000 if you want it for free … ).
I think we will get problems/questions to this for the default weather module too.
So (for default weather module) if you use endpoints weather and forecast and old onecall v2.5 everthing works out of the box with old api keys, if someone use new onecall v3.0 he needs an api key for 3.0 and has to set apiVersion: "3.0", in the config …