Besides GPS, the GNSS currently includes other satellite navigation systems, such as the Russian GLONASS, and may soon include others such as the European Union’s Galileo and China’s Beidou.
"The map uses are color coded overlay to indicate low (green) to high (red) levels of interference with global navigation satellite systems (GNSS). Often just referred to as GPS, there are actually multiple systems beside the US GPS constellation, such as Russia’s GLONASS, Europe’s Galileo, China’s BeiDou, and others."
But aviation is much more conservative due to its safety-critical nature. Galileo was only just recently (2023) certified for use in aircraft systems by ICAO:
https://www.esa.int/Applications/Navigation/Galileo/Galileo_...
The redundancy of multiple independent GNSS systems is a fine thing for dealing with unintentional failures, of course.
Just for the record, this must have been written ages ago. Today you would rather look up to NavIC joining them as a global system and QZSS operating independently from GPS soon.