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Nighthawk CAX80 - How to whitelist a specific MAC address for incoming VPN connections

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I just upgraded my old NetGear Cable Modem / WiFi Router to a new NightHawk CAX80 and now *some* of my VPN connected devices won't work any longer.

I duplicated all the port forwarding rules, including ports 1701, 500, and 4500 to my Windows Server 2019 where I have the L2TP set up and working (not changed as part of the router upgrade).

Now my daughter's laptop (she's connecting from another location) works perfectly with the VPN connection still, but my laptop refuses to work any longer, giving error message "The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer". Note that I'm testing this out by using my AT&T WiFi hotspot device to connect my laptop to the Internet before testing the VPN, which has worked in the past as a valid way to test out external connections via VPN. Just as an additional observation, one time when testing I forgot to connect to my AT&T WiFi hotspot and left it connected to my Netgear internal WiFi and the VPN connected successfully, changing my IP to one within the range of the configured virtual VPN IP Addresses. Because of this I know the issue isn't related to an incorrect password or shared secret.

I googled this error some but only found articles from early last year stating that a KB update was causing this and shows how to revert the update or apply the subsequent fix from early 2022.

I checked the logs on the VPN Server and it doesn't even look like the traffic is making it to the Windows server 2019 (it must be being blocked by the router). I can't see anything useful in the router's log. Does anyone know how to add a specific computer (MAC address) to the ACL for this router to force it to accept connections from my laptop or whitelist it? Also, where can I locate the log that actually shows the traffic being rejected? I couldn't find it in the iPhone NightHawk app under "Threats".

Any advice would be greatly appreciated.
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