Based on the below, I reinstalled Big Sur, but it didn't make any difference.
Here's what I see in /var/log/ppp.log, the memory message looks suspicious?
Thu Dec 15 10:51:44 2022 : publish_entry SCDSet() failed: Success!
Thu Dec 15 10:51:44 2022 : publish_entry SCDSet() failed: Success!
Thu Dec 15 10:51:44 2022 : l2tp_get_router_address
Thu Dec 15 10:51:44 2022 : l2tp_get_router_address ***.***.***.*** from dict 1
Thu Dec 15 10:51:44 2022 : L2TP connecting to server ‘***.******.com' (***.***.***.***)…
Thu Dec 15 10:51:44 2022 : L2TP can't set L2TP server address: Cannot allocate memory
Thu Dec 15 10:51:44 2022 : IPSec connection started
Thu Dec 15 10:51:44 2022 : L2TP error sending Hello (Destination address required)
Thu Dec 15 10:51:44 2022 : Failed to send L2TP hello trigger. tried 0, max 10
Thu Dec 15 10:51:45 2022 : L2TP error sending Hello (Destination address required)
Thu Dec 15 10:51:45 2022 : Failed to send L2TP hello trigger. tried 0, max 10
Thu Dec 15 10:51:46 2022 : L2TP error sending Hello (Destination address required)
Thu Dec 15 10:51:46 2022 : Failed to send L2TP hello trigger. tried 0, max 10
Thu Dec 15 10:51:47 2022 : L2TP error sending Hello (Destination address required)
Thu Dec 15 10:51:47 2022 : Failed to send L2TP hello trigger. tried 0, max 10
Thu Dec 15 10:51:48 2022 : L2TP error sending Hello (Destination address required)
Thu Dec 15 10:51:48 2022 : Failed to send L2TP hello trigger. tried 0, max 10
Thu Dec 15 10:51:49 2022 : IPSec connection failed