It sounds like a routing problem, so either the vpn client does not know where to send packets for dst 192.168.88.0/x or internal devices does not know where to send these back to, doubt it is the latter though as they should have a default gateway if they access the internet.
Make sure you have a route on the VPN client to dst via vpn interface by either enabling “Use default gateway on remote network” if it is a Windows client, or adding routes manually