Actually, OpenSSH has built-in TUN/TAP support using -w<local-tun-number>:<remote-tun-number>. You can create a layer 3/point-to-point/ TUN tunnel or layer 2/ethernet/TAP tunnel.
I used to run a site-to-site VPN between two sites a couple of decades ago with a simple script doing just this. These days we'd use OpenVPN or strongSwan for such use-cases but despite the 'hackiness' of the former approach, it worked reliably for years.
OpenSSH VPNs suffer from TCP-over-TCP [1]. I'd only use them as a last resort.
Sometimes I actually wish SSH would offer UDP support for precisely this use case, but arguably, TCP VPN support is already a stretch in terms of scope for SSH.
I used to run a site-to-site VPN between two sites a couple of decades ago with a simple script doing just this. These days we'd use OpenVPN or strongSwan for such use-cases but despite the 'hackiness' of the former approach, it worked reliably for years.