Can’t remove “synchronizing/suspect” database after removed from availability group Sql Server 2019 Enterprise

I’ve removed a db from a synchronous availability group.The db shows "synchronizing/suspect" as it should. I’m trying to remove this database cannot. I have tried:

DROP DATABASE [db1]; 

but get "Cannot drop database "db1" because it is currently in use.". even though their are no sessions using this database.

ALTER DATABASE [db1] SET OFFLINE; 

but get "ALTER DATABASE failed because a lock could not be placed on database ‘db1’. Try again later."

ALTER DATABASE [db1] SET SINGLE_USER WITH ROLLBACK IMMEDIATE 

but get "ALTER DATABASE failed because a lock could not be placed on database ‘db1’. Try again later."

ALTER DATABASE [db1] SET EMERGENCY; 

ALTER DATABASE failed because a lock could not be placed on database ‘db1’. Try again later.

This is a 24/7 production db and restarting is not a good option.

Any advice?