A little added info, if I try to ping 192.168.1.10 (Test Client 1) from 192.168.1.20 (Test Client 2) while running tcpdump on both pfsense, I see ARP traffic:
[2.4.5-RELEASE][root@TestFW01.localdomain]/root: tcpdump -nibridge0 host 192.168.1.20
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on bridge0, link-type EN10MB (Ethernet), capture size 262144 bytes
08:48:23.031203 ARP, Request who-has 192.168.1.1 tell 192.168.1.20, length 46
08:48:24.028594 ARP, Request who-has 192.168.1.1 tell 192.168.1.20, length 46
08:48:25.028870 ARP, Request who-has 192.168.1.1 tell 192.168.1.20, length 46
[2.4.5-RELEASE][root@TestFW02.localdomain]/root: tcpdump -nibridge0 host 192.168.1.20
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on bridge0, link-type EN10MB (Ethernet), capture size 262144 bytes
08:48:33.036875 ARP, Request who-has 192.168.1.1 tell 192.168.1.20, length 46
08:48:33.037605 ARP, Reply 192.168.1.1 is-at 00:bd:79:1a:ff:01, length 28
08:48:34.036904 ARP, Request who-has 192.168.1.1 tell 192.168.1.20, length 46
08:48:34.037940 ARP, Reply 192.168.1.1 is-at 00:bd:79:1a:ff:01, length 28
If I run the same tcpdump command, substituting the ovpn interface for bridge0, I see ARP requests and replies on both pfsense.
I'm not sure who is the owner of 00:bd:79:1a:ff:01, but it doesn't appear in the ARP table of either pfsense, and I get no result for it on either hwaddress.com or maclookup.app.
edit: typo