In 20w22a some select users experienced the bug MC-186284, which turned these players' vision upside down. This bug has since been closed and marked "fixed". While these players at first don't experience this bug anymore, when the graphics setting is changed to "Fabulous!", the bug reemerges.
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What are your system specs?
I added some pictures to display the issue at work, as well as my system specs. There is a lot more info in the original bug report I linked In the post. I don't want to copy everyone else's comments, info, and contributions though.
Confirmed for 1.16-pre3
Cannot reproduce in 1.16-pre3 on Windows w/ NVIDIA GeForce GTX 1050 Ti

Your system does not seem to meet the minimum requirements to run Minecraft. The following requirement seems to not be met: RAM
What? I have 8 gigs! Thats above minimum requirements

Mem: 85% 1337/2048MB
2048MB = 2GB?
Or am I a complete derp?
Edit: The latter.
I believe that shows the amount of RAM allocated to MC, which is usually 2GB
Confirmed for pre-release 5

@unknown - do you (or anyone else) get a warning message when you try to switch to Fabulous graphics?
Yes, I do. The first time I checked for Pre-release 5, I opened a world already on fabulous to test it out, which means I never got the warning. Upon retrying, I do get the message. I believe that means this issue is resolved and no longer necessary.

Thanks for getting back so swiftly @unknown!