From Garmin, though without a breakdown of proportion of devices:
In addition to GPS, Garmin products utilize other global navigation satellite systems (GNSS) including the Russian Global Navigation Satellite System (GLONASS), the European Union Galileo system (Galileo), and the Chinese BeiDou Navigation Satellite System (BDS), and satellite based augmentation systems (SBAS) including the U.S. Wide Area Augmentation System (WAAS), the Japanese MTSAT-based Satellite Augmentation System (MSAS) and Quasi-Zenith Satellite System (QZSS), and the European Geostationary Navigation Overlay Service (EGNOS) aviation Safety of Life (SoL) service.
Though to the extent this is a US-centric site, the other reason for not caring much about Beidou is that the FCC still has a geofence block for Beidou, so that no signals may be used in US territory: https://www.gps.gov/spectrum/foreign/. It's as if Beidou doesn't exist in the US, and even a receiver that supports it will only start using the signal once it first confirms through other GNSS's that it's not located in US. (Example: most phones made in the last 3-5 years)
I have a recently-introduced Garmin model focused on multi-GNSS (gpsmap 66sr) and it only does GPS, GLONASS and Galileo. So I fear that that is mostly marketing copy from Garmin.
In addition to GPS, Garmin products utilize other global navigation satellite systems (GNSS) including the Russian Global Navigation Satellite System (GLONASS), the European Union Galileo system (Galileo), and the Chinese BeiDou Navigation Satellite System (BDS), and satellite based augmentation systems (SBAS) including the U.S. Wide Area Augmentation System (WAAS), the Japanese MTSAT-based Satellite Augmentation System (MSAS) and Quasi-Zenith Satellite System (QZSS), and the European Geostationary Navigation Overlay Service (EGNOS) aviation Safety of Life (SoL) service.
Though to the extent this is a US-centric site, the other reason for not caring much about Beidou is that the FCC still has a geofence block for Beidou, so that no signals may be used in US territory: https://www.gps.gov/spectrum/foreign/. It's as if Beidou doesn't exist in the US, and even a receiver that supports it will only start using the signal once it first confirms through other GNSS's that it's not located in US. (Example: most phones made in the last 3-5 years)