Video is of just the Inventory Screen but this does happen with all UI in the game.
Flickering also occurs when nothing is being done in the inventory screen but a screen capture is unable to capture it for some reason (most likely too quick for a screen capture to record it)
you are not alone.
This is occurring with me too. I was worried it was my video card, but the flickering does not occur on my other PC games such as Cities skylines. and it doesnt occur with youtube videos, screen savers or internet browsers. it is JUST minecraft and it only started with the 1.20 update.