I've been experiencing increasing lag/delay in my world when:

• mining/placing blocks - blocks render delayed after they are mined etc; the game registers that blocks have been mined, only rendering is delayed (it's not like ghost blocks or other types of lag, its purely visual)
• light updates and basically everything that's related to changing the world can be randomly delayed when building, mining etc.
• opening chests, shulkers, inventories is often delayed for a second 
• sounds sometimes play delayed

This issue started not too long ago, likely within one of the 1.21 udpates. World is about 870 mb, normal survival mode and nothing that could cause the lag. Device is good enough to run the game lag-free.

Can't find a cause unfortunately. Not related to autosave and seems to happen randomly. Can't reproduce on a basic flat world, only happens on my bigger old world. 

See the attached clip. Doesn't need to be flying or walking for it to happen.