Describe the bug
Well, what can I say - crashreport is here. It dosn't happen when Obfuscate, Furniture and Vehicles aren't present.

Crash report
pastebin

Please complete the following information:

• Minecraft Version: 1.16.4
• Mod Version: Everything latest at the time of writing

Remove Optifine.

Remove Optifine.

Well, as much as I'd like to, there's no real alternative or at least I'm not aware of any - OF gives tremendous amout of settings and a huge performance boost :/

Optifine in any version 1.13+ does not give any real performance boost, it just renders less chunks. If you want the same performance boost Optifine gives then lower your render distance.

Removing it is the only way to fix this issue as it's an incompatibility between the two

This is an Obfuscate mod issue, not the Furniture Mod. I am going to take a look into it soon.