PT 1 - copying my buildings and farms over the new world buildings to fix the disrupted inventory.
MCA Selector is an "external tool to export or delete selected chunks and regions from a world save of Minecraft Java Edition" github.com/Querz/mcaselector
I updated my experimental world (fullbright resource pack from vanilla tweaks) to 1.20.6 and found fullbright did not work. So, I restarted in 1.20.4, the original world, and lost all of my inventory, armor, and anything in a chest, which was quite substantial. Since I didn't want to go through the hard work of acquiring these things, I used MCA Selector to copy and past from a backup world, because I did want to use 1.20.6 even if it didn't have fullbright resource pack. This was because I reverted back to 1.20.4. Minecraft does state that using experimental objects can disrupt the world. Either way, I lost all of my inventory, everywhere.
I hope you can use this tool to save your worlds and inventory that got corrupted somehow.
Remember Technoblade / @technoblade