First off: It will not allow me to change to say only Affects Versions to 1.20, as this is the version I am playing on that I saw this bug. However, there are only 2 options "1.20.1" and "1.20.2 Pre-release 2." So I generated a 1.20.1 and they are still off.
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I use litematica. A mod that allows you to build things from one world to another, including servers. So, making sure the spot is right, for me, is important. More so if I'm adding onto to an existing build, I always go by cords to line up the build grid. However, the X cords and Z cords of both regular F3 Cords and the Targeted Block Cords are off by 1 block. Now, it isn't much, probably not worth wasting time on it, but it becomes tricky to align a build up when it's constantly one block off.

This happens in both in Single player (regardless of gamemode) and Server (again regardless of gamemode).

Polished Andesite screenshot is Version 1.20 - Modded - Off by 1 block
Grass screenshot is Version 1.20 - Not Modded - Off by 1 block
Red Sand screenshot is Version 1.20.1 - Not Modded - Off by 1 block