I take it Legends of Runeterra doesn't work for you? It's pretty F2P friendly in my experience but then I only really play the Path of Champions mode these days. I guess you do have to grind for expansions though.
I think Elder Scrolls Legends is still running but they aren't releasing new cards so once you have them all, you're done. I could be wrong.
Gwent is in a similar position, might be the last year of card releases before they democratize the meta. Don't follow closely but I think that's the case.
If you like Slay the Spire, Monster Train is also very good.