You could also use zrok.io. It’s an open source alternative which can be self-hosted or has a free SaaS. It also includes cool features like ‘private sharing’ (which means both sides can be private with no inbound ports). I work on the parent project.
It’s not free, though, at least $20/year on pro. Why not just pick a Ngrok alternative which can provide a fixed IP - https://github.com/anderspitman/awesome-tunneling
I was going to share the same link but you beat me :D
I work on one mentioned, zrok.io which is both open source and has a free SaaS.
zrok.io using the free SaaS together with 0Auth - https://blog.openziti.io/the-zrok-oauth-public-frontend