I'm glad that you think the UI indirectly hints that there is a limit to what pieces you can place. I like to teach players without words whenever I can, so even though I have a tutorial, I didn't cover absolutely everything in the game.

I agree though that there is a stale meta I've learned through my own playtesting. The game is much more interesting in the early rounds, as you don't have enough mana and thus have to be smart on what pieces to place and move. However, once you get a full column of 8 pawns, you can decimate most waves with ease. I see two causes of this:

1.  Enemy variety. The only COVET currently in the game moves in a straight line and takes 10 shots to destroy. Even in mass numbers, it isn't much of a threat.
   For the future, I've planned to introduce an "armored" COVET which has considerably more HP (think Conehead Zombie in Plants vs Zombies). However, I was initially planning to introduce this enemy a few levels into the game, as I would first add a different enemy type which is just as fragile as the demo COVET. Now I am convinced to swap places and include the armored COVET as soon as possible, to counter the 8-pawn strategy.
2. The economy. Currently, the king produces 50 mana per 5 seconds. That means in 40 seconds, you can set up a full column of 8 pawns.
   I have a few ideas on nerfing the economy, not just to enforce the earlygame strategies for a longer period of time, but also to encourage a future mechanic where pawns can be upgraded into free pieces of other types.

My workspace is a 64-bit Windows 10 on relatively old hardware. I have been consistently able to run the game under these conditions, so unfortunately, I wouldn't know off the top of my head why this is happening to you.

I will upload a 32-bit version of the game as soon as possible, in case it is the bits which are throwing you off. If that doesn't work either, tell me and I will ship a third version of the game with Godot's debugger, so we could possibly figure out exactly why it's crashing for you.