I am building a PC with a Ryzen 5 1600x and an RX570, with a B350 motherboard. Will this support windows 11 install from an external drive?
With a B350 motherboard you will probably have to upgrade the bios to the latest version.
Ryzen 5 1600 is not on the compatible list, ryzen 5 2600 is, but the 1600 would run fine once windows 11 is loaded. AMD cpu's have the tpm function internal, in the bios go to advanced section to enable the tpm.
A couple times I installed the approved CPU, loaded win-11 than later put a 5-1600 in with no problems. The biggest problem you may have is getting secure boot enabled properly.
In my experience the main drive needs to be a .gpt drive, not a ntfs drive, then install win-11, enable uefi boot mode.
to check if the TPM is active , run tpm.msc , and it will tell you.