So, 2 months later I got an answer!

to the one that asked why Iadded a global.json
https://learn.microsoft.com/en-us/dotnet/core/compatibility/sdk/10.0/nu1015-packagereference-version this is why
to force a LOWER sdk
...
(had a problem with a breaking change between net 8 and 9 when both were stable, this is just yet another example )