The patch is rather big, the central feature is being able to custom-build your own level to play in. But beyond that there's massive rebalancing to dandelions, healing items, 3-hit combos, 2H weapons, enemy wave retaliation attacks, MIX.Rs, everything.
Also, Grounded is free to try out for the next 2 days (as of me writing this): https://store.steampowered.com/app/962130/Grounded/
This game was so polished all the way to the end. I think it didnt need an update, but this type of content is a big deal because the custom worlds will mean it has content forever