Ender 3 unknown (maybe bed leveling) issue
Non-square gantry is a common problem with the Ender 3. You should be able to compensate by adjusting the bed leveling screws so that the nozzle at Z=0 is touching the bed at each of the four adjustment points. This will leave some skew, which you may or may not care about. But the right thing to do is leveling the gantry.
Both sides' Z carriages have some play in how the gantry mounts to them - the holes are larger than the machine screws that go through them - so after loosening the screws you can make adjustments. The screws on the side with the Z motor are hidden between the carriage and Z axis extrusion it rolls on, so to adjust it you need to roll the whole assembly off the top of the printer (with the cross beam at the top removed). Since you can't tighten it in-place, you just have to do your best to get it straight before putting it back on. The unpowered side, however, has screws that are reachable with the whole assembly in place, so you can square the gantry with the Z extrusions before tightening them.
Keep in mind that the whole Z axis system is severely over-constrained, with 6 wheels where 3 should suffice to constrain it. People have a lot of different ideas about how you should deal with this, and I'm still not sure what's best, but I think you want to get each of the V-roller sets tight (using the eccentric nuts to adjust the inner wheels) before leveling and tightening down the gantry. Otherwise the wheels may have uneven tension, causing the assembly to want to twist.