Hello Mike,
Yes, your understanding of PSK is correct. I would recommend using PSK with ECDHE for this reason, if feasible. TLS 1.3 does generally offer forward secrecy, but there are cases where you would want to use PSK only, so it is still offered despite not offering forward secrecy.
You can turn on debug logging in wolfSSL to confirm the key exchange and connection are being completed as expected by building wolfSSL with --enable-debug. You could also capture a packet dump and open it with Wireshark to confirm everything being sent and received matches your expectations.
You may find our PSK examples and documentation here helpful: https://github.com/wolfSSL/wolfssl-exam … master/psk
Thanks,
Kareem