All blocks vanish with nothing but void visible when using the hammer -Only while trying to break blocks, all blocks reappear after you either break the blocks or stop mining-, disabled shaders and texture pack to be sure those were not the cause. :

Did not cause a crash:

Versions:

• Minecraft: 1.16.5
• Forge: 36.1.0
• Mantle: 1.6.88
• Tinkers Construct: 1.16.5-3.0.2.78

Confirm below that this issue is not covered on the roadmap or "Whats New?"

Can it be reproduced with just Tinkers Construct? If not, list the other mods required to reproduce the issue.
This issue is replicated with just Tinkers and Mantle.

Should be fewer than 10 mods, you should be running no mods besides those 10 when you reproduce the issue.

Did you remove optifine as well

Looks like a duplicate of #4316 to me.

Closing for lack of information, going to assume its an optifine bug