i am unable to say wether this happens in 20w11a as the minor generation changes have invalidated the seed as an example of the bug and due to the specific nature of the bug, i cannot replicate it
21w10a you dont have to do it quickly you can take all the time you want
also happens less often with gold
have you been using any special clients previous to this hacked clients or anything with fullbright as these can change your brightness cross versions
you can get it to run it is just complicated id recommend pi-apps for installation of java mc runnable on pi however it will still be snails pace but this is something i think should be changed as many people can improve the pi to run faster obsoleting an entire platform isn't really very in line with mojangs business ethic i believe that this should be added as a feature and there is a vote here as someone who's first computer was a pi and first Minecraft was the (now completely unsupported) raspberry pi edition this topic is very close to my heart if you too would like pi support of java officially there is a suggestion and petition here https://feedback.minecraft.net/hc/en-us/community/posts/360075486052-Port-the-latest-Java-Minecraft-Launcher-to-the-Raspberry-Pi
the server i am playing on is using fabric however i couldn't find anything to suggest this was the reason for the bug as it happens vice versa on vanilla servers with the icons and not in game i will attach more examples with f3 open as soon as i can find more instances of this bug
the singleplayer world was a non modified environment the multiplayer was modified server side not client side