Didn't think to add a screenshot, so here it is:

https://gtm.you1.cn/sharedfiles/filedetails/?id=3256988118

You can see the icon in the bottom right, under Back in the footer. Holding the same button (either Steam or Quick Access) moves the icon along the bottom of the screen. I've also since remembered where I've seen the icon before, it's the same icon you get when resizing windows in desktop mode.

Did you enable an animation to play when "Waking" from sleep mode?

I didn't even know that was a thing. I only have boot and suspend animations. All are local files and were randomised with the Animation Changer Decky plugin, but are now randomised with the built in Shuffle feature (in Customise).

I'm still running Decky-less and it's still happening. I can't find a pattern as to when it happens, it's totally random so far. The menus can load from a cold boot when immediately pressing one of the buttons, or I can wait a bit another time and they don't, in and out of games or in a game for a while they can load, or another time they don't (after loading from cold boot), suspending and waking sometimes they load, sometimes they don't, after working before the suspend. Plus any other combination I've missed.

Just to mention, when they don't show, they haven't then started showing later on. Maybe I haven't left it long enough, but only a reboot will make them show again, then the figurative 'when it'll stop working' randomised wheel is spun again.

Sorry, I tell a lie. I did know it was there, it's right under the Shuffle boot animations toggle, but still no I haven't turned it on (ever, I don't think)

I still have this problem. I've reinstalled Decky because it does not cause the problem, it's there regardless of whether Decky is installed. It's really bugging me now!

I've just figured out what was causing this problem for me. The deadzone was too low on my right thumbstick (which sometimes doesn't recentre properly) therefore pressing either the Steam button or Quick Access button would register as the combination for joystick mouse on screen and obviously not bring up the respective menu. Upping the deadzone a step will surely fix the problem. And yes I have Guilikit Hall Effect joysticks.