Yes, I have a Pi4 booting off a SSD on a USB-SATA bridge. No SD card installed. This graduated from beta about a year ago. [1]
Btw, since you brought up USB: disable UAS [2] when using cheap USB-SATA bridges! UAS is regularly recommended for performance reasons, but I've gotten block-level errors (eg those below) and filesystem corruption with UAS multiple times and never with UAS disabled. I've seen enough similar reports on the Internet to think it's better to just disable UAS.
The Linux kernel has explicitly disabled UAS for some of these chipsets, but clearly not all of the offending ones. I'm not sure what you'd have to do to be confident your chipset is safe. I just don't think it's worth it.
Btw, since you brought up USB: disable UAS [2] when using cheap USB-SATA bridges! UAS is regularly recommended for performance reasons, but I've gotten block-level errors (eg those below) and filesystem corruption with UAS multiple times and never with UAS disabled. I've seen enough similar reports on the Internet to think it's better to just disable UAS.
The Linux kernel has explicitly disabled UAS for some of these chipsets, but clearly not all of the offending ones. I'm not sure what you'd have to do to be confident your chipset is safe. I just don't think it's worth it.[1] https://github.com/raspberrypi/documentation/commit/bfef967d...
[2] https://github.com/scottlamb/moonfire-nvr/wiki/System-setup#...