Hello,
I use vpn and internet.
I suggest with other guy, to Ubuntu be able to choose witch process is able to access to internet or VPN, witch files or disk.
Look:
https://forums.openvpn.net/viewtopic.php?f=1&t=26791&p=80593#p80593
Bye
_absynteZero2018_SP
This kind of outbound firewall or port selector gets suggested a couple times each year.
There are several ways to accomplish this (IPTables, AppArmor, Snap confinement, etc), though none are simple and several are rather different than what you seem to envision.
Generally, best practice is to be judicious with your selection of networking applications.
If you want help learning how to use IPTables to deny outbound packets, please seek help in the Technical Support venues.
If you wish to develop and contribute a realistic solution to Ubuntu, start at https://developer.ubuntu.com.
If you have designed a realistic, achievable feature to add to an existing application, please file a wishlist bug against that application. Working code would be very helpful.