When I use the trowel, the blocks I place just disappear, and I don't know why. And the tape measure doesn't craft for some reason.

Some questions just to get more info:

• Which minecraft version and datapack version are you using?
• Are you using any other datapacks or mods?
• Does this occur on a singleplayer world or on a server?

• Which minecraft version and datapack version are you using?
  I'm using Fabric 1.21.1
• Are you using any other datapacks or mods?
  I'm only using other mods
• Does this occur on a singleplayer world or on a server?
  occur on my LAN server.

The tape measure was only added in 1.7, which is for 1.21.3 you won't be able to get the tape measure without updating

As for the trowel, it's likely one of your other mods are causing the blocks to disappear, possibly some kind of party/claims mod?

These items have been backported in the latest 1.21.1!