@Stuart Weenig - I was reading the Checkpoint article it mention about to monitor state of the VPN tunnel via SNMP OID 1.3.6.1.4.1.2620.500.9002.1.3 and SNMP OID 1.3.6.1.4.1.2620.500.9003.1.3. I don’t think those OID is added in the Checkpoint core.
Here the link for the article.
https://support.checkpoint.com/results/sk/sk63663