How many games?

Is there a limit of how many games can be in a Scid database?

I dont think so.

But if your base is very large, I find it takes a few seconds for the tree to update after entering a move, so I suppose it is limited by your hardware resources.

I have one DB over 1/2 million games, sometimes it takes a bit for trees, compact DB & stuff like that.   I haven't noticed any issues using the search function with large DB.

Only issue is if you filter the DB then mark a game to be deleted & delete the game under the filter.  Occaasionally things get wierd.   If the filter is on & I mark a game to be deleted I  then reset the DB then run the compact DB to accomplish the delete.