After thinking about it for a moment, if you don’t want to pay for a VPS, I think you can run a hidden service with Tor then just use the onion address to ssh back into the computer. I found this guide. I haven’t done it, but it seems like it should work.
I just use autossh for it.
I run an ssh connection to a VPS I pay like $5, which forwards a port there. The screen in the following command isn’t required, but I have it so I don’t have to keep the terminal window open.
screen -d -m -S autossh.eastusa.keepalive autossh -M 33333 -R VPS_IP_HERE:5555:localhost:22 root@VPS_IP_HERE
Then from other computers, to connect back
ssh -L 5555:localhost:5555 root@VPS_IP_HERE
ssh root@localhost -p 5555
For remote computers connecting back, the first ssh connects to the VPS and forwards a port to the remote computer. Then the 2nd ssh connection uses the forwarded port to complete the ssh connection to the computer behind the IP that can’t port forward.
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