tikituki - if it helps, I had a friend on PS4 join my world and it looks perfectly fine to him. Looks like it's just a graphical issue, but I'd recommend backing up your worlds anyways!
Looks like we're all suffering the same issue. I put all of the info I've got here: https://bugs.mojang.com/browse/MCPE-109904?focusedCommentId=859020&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-859020
I'm experiencing the same issue - I understand others here are reporting similar bugs.
Here's the info I've gotten so far:
Reinstalling Minecraft doesn't fix this, updating graphical drivers doesn't fix this.
The buttons still work, I managed to find the UI reader and using that I've managed to navigate the menus.
Seemingly randomly while navigating the menus, the UI sometimes returned. The first time this happened was when I entered the marketplace, then again when I entered the realms menu, the third time this happened was when I used the UI reader to navigate to "UI Profile" in the Video Settings and selecting "Classic" - this seems to reset the UI and is the only way I've been able to repeatably bring the menu up.
Upon logging into a world, I get the weird graphical issue that I've seen others having, with textures all over the place - I've uploaded an additional video and picture. Turning on/off smooth lighting appears to temporarily make the issue slightly better before slowly getting worse and worse.
By the looks of things, the raytracing has completely screwed with certain peoples' graphics - even though I'm not on a raytracing enabled world and have raytracing switched off. I'm at a loss as to how this is affecting the start menu, but I can confirm with certainty that Minecraft worked perfectly well minutes before I updated, so it's definitely this raytracing update that's doing it.
It's also worth noting I had a friend on ps4 join my game, and it all looks fine to him - so our worlds appear to be safe, this is strictly a graphical issue.
I guess we just have to hold tight and wait for a patch - at present Minecraft is completely unplayable even after getting through the menu!
The menu works fully - I managed to get UI reader working and through that I was able to navigate the menu. By going into graphical settings and selecting "UI Profile" -> "Classic", it appears to reset the UI and you'll (hopefully) be able to see the menu again. Unfortunately graphical issues in the game make it practically unplayable until they fix the bug anyway.
I've put down all the info I have here: https://bugs.mojang.com/browse/MCPE-109904?focusedCommentId=859020&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-859020