Hello I am using a GL-E750V2 with OpenVPN and Layer 2 Configuration. The same configuration works on a GL-MT300N-V2. It does not work on the GL-E750V2. In LuCI I have the OpenVPN Client installed -> luci-app-openvpn git-23.093.42303-4b07c72 12.47 KiB LuCI Support for OpenVPN Installed.
On the MT300NV2, it looks like there is tun plugin, so you can test whether it can work in TAP.
Since probably beyond the GL functions which I mean regarding these third-party plugins, so it requires actual config to verify to test if it works.
The XE300 is not supported, and the version needs to be updated to 4.6 later.
Like the MT3000, AXT1800, SFT1200, etc. have been updated to the firmware version after 4.6.
In the later period, there are firmware updates for the MT300NV2/ E750V2, so I assume it will support TAP when they got 4.6. Please await first to see the new firmware if the TAP feature is supported (evaluating whether the performance of these models is sufficient) instead of buying new routers.