I could not find any other issues with this problem, tried searching. Sorry if it is a duplicate.
The anvil window which opens when right-clicking the anvil does not open if the vanilla datapack is disabled. I know disabling datapacks is going to start affecting the game (like with leaf decay), but I decided to report this since every other block with a window still works with the datapack disabled. All three variants of the anvil are affected.
Blocks I tested that still worked: Crafting table, furnace, chest, ender chest, brewing stand, beacon, dropper, dispenser, hopper, minecart with chest, minecart with hopper, trapped chest, enchanting table.
Sometimes if you spam-click it will open for a fraction of a second then disappear right away again.
This was only tested in a singleplayer world.