When i start up minecraft i get a black screen for around 30 seconds or sometimes 1 min / 50 to 90 seconds
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This sounds very similar to MCPE-84857, but is probably different, as by your description the game eventually loads, correct?
Do you get any loading screens whatsoever (red, mojang logo, % bar), or does the game launch immediately on a back screen? Please make sure your graphics drivers and system up are up-to-date.
If you use task manager, do you see any excessive use of any form of data?
I'm unable to reproduce this as of 1.21.2. Is this still an issue? If so, are you using any resource packs? Does reinstalling the game help (you can backup your worlds by going to %localappdata%\Packages\Microsoft.MinecraftUWP_8wekyb3d8bbwe\LocalState\games\com.mojang\minecraftWorlds
and copying the folders there)?
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