What Datum does GPS use? Or Galileo, Or Glonass, Or Beidou?

[Jim bell]

The Datum I would guess is WGS-84, but I am looking into possibly using NATRF2022 fpr a specific purpose, and I don't know whether I should use it or WGS-84.

The difference between these Datums is presumably quite small, but I am preparing to set various homebrew brass benchmarks at various intersections of even Latitude and Longitude lines in the Pacific Northwest, and I would like to set them to an accuracy primarily limited by my ZED-F9P, which when using RTK corrections os roughly14 millimeters.  

The differences between these various Datums is typically larger than this.This is a conversion tool between some of these Datums.

https://www.ngs.noaa.gov/NCAT/

But, this tool makes no reference to WGS-84 or to NATRF2022.

[Knut]

https://gssc.esa.int/navipedia/index.php/Reference_Frames_in_GNSS