Since 1.16 has come out, there has been lag attributed to a lot of things. My observation has to do with lag with repeating redstone. I have observed this in both a single player world, and on a server running BDS. My specific example has me using a portal ticking gold farm. Prior to 1.16 you could run 4 portals on a fast clock, and tick them in rapid succession to spawn a lot of pigmen in quickly. Now, you can use this same clock to tick 1 portal without lag, but increasing to more than 1 will slow the redstone down to a slow pace. Ive had to move to a 4 tick delay for 4 portals for them to not lag. Other designs I have seen are doing this as well, and reports of running any sort of repeating redstone alongside trident killers is doing this as well.