At this point, do not expect the R5b to work reliably.
It is best not to use a USB-PD power supply but any ~12-20V supply with an to USB-C adaptor.
if you do not need more than the bare board something like a 5V 3-4A power supply might also work out fine but once you use USB-devices and maybe M.2 cards that will quickly become an issue.
Radxa is so far doing a really bad job communicating about these issues but there are still quite a few issues.
Funnily enough I also have a NanoPi R6s and while having less features, it also has a lot less issues due to reduced complexity.