I know free vpns aren’t it normally safe but everywhere I look about this one people are talking about it positively.
Softether is an opensource VPN system being open source means its code is transparent and its also self hosted meaning you would be running your own server so you have full control of all hardware so the safety of the vpn depends entirely on your configuration settings. If you dont know what you are doing and configure it poorly someone could hack it but other than that its not going to be spying or stealing your data
SoftEther is a program with a variety of VPN protocols, which in addition is open source, has an excellent reputation and shows itself only from the best side. You can say that this software is similar to OpenVPN or WireGuard applications.
SoftEther is not a VPN service that charges you for the service, usually for SoftEther you rent a server where SoftEther will be configured, of course, there is the VPNGate project where SoftEther servers are hosted, but it is quite different.
So, to answer your question - yes, SoftEther is quite safe to use (if you follow the norms of setup and use).