SUMMARY
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Openfortivpn connection is established apparently, routes are created, but the connection is unusable, can't reach any of the services behind the VPN, ping them does not work. The connection seems to be established, as reported by the Network Manager applet, but will disconnect after a while, like 10-20 mins (may there be a timeout, actually?).
It worked fine previously to this Network Manager version.
Using openfortivpn cli works perfectly, so there may be its integration with the Network Manager affected (well, on both sides...).

STEPS TO REPRODUCE
1.  Establish a openfortivpn connection with Network Manager
2.  Observe the connection is reported as "connected"
3.  Try to access any service behind the connection - no availability
4. Wait, the connection will go "disconnected" state by itself in 10-20 mins.

OBSERVED RESULT
- No service on that VPN connection can be accessed by any means - ping, putty, ssh, remote (RDP)
- The connection will disconnect automatically after a while
- Checking the routes and DNS servers, they are created/added

EXPECTED RESULT
The connection is setup, lasts and the services behind that VPN are accessible.

SOFTWARE/OS VERSIONS
Operating System: MocaccinoOS 
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.9
Kernel Version: 6.1.38-mocaccino (64-bit)
Graphics Platform: X11
Processors: 16 × 11th Gen Intel® Core™ i7-11700K @ 3.60GHz
Memory: 61.6 GiB of RAM
Graphics Processor: NVIDIA GeForce GTX 1060 6GB/PCIe/SSE2
Manufacturer: ASUS

ADDITIONAL INFORMATION
Openfortivpn bug reports:
https://github.com/adrienverge/openfortivpn/issues/1128
https://github.com/adrienverge/openfortivpn/issues/1120