"""
****************** Blame Report 1.9.2 ******************

A crash is most likely going to happen right after this report!
It seems flying_end_ship | majruszs_difficulty:flying_end_ship is the cause because it is not added
to the FlatGenerationSettings.STRUCTURES map. Please let the mod owner
of that structure know about this crash. That way they can add their structure
to that map since someone is trying to spawn it in a flat/custom dimension.
"""

[21:17:08] [Render thread/ERROR] [minecraft/SaveFormat]: Exception reading C:\Users\nicho\Games\multi-mc-minecraft-launcher\mmc-stable-win32\MultiMC\instances\1.16.5.minecraft\saves\New World\level.dat
java.lang.NullPointerException: null

Thanks for reporting this bug, it will be fixed in the next update.