Coordinate reference systems (CRS)
Geographic coordinate systems. Unit in degrees, angular surface, represented as latitude longitude. Commonly used for GPS. 90 to -90 degree for latitude and 0 to 180 for longitude.
Projected coordinate systems. Unit in meters, flat surface. Commonly used for XYZ map tiles, not fully cover entire earth surface.
Scale of XYZ tiles will depend on the size of your project (QGIS window) and monitor. If you arrange a single row of menu icons on 1080p monitors, you likely will have similar viewport as mine.
Best at 1:22,244, 1:44,490 (divide or multiply by 2, may have slight difference at different areas or when panning is performed.