Authentik! i've been using it since over a year and its been a wonderful experience. supports many protocols and is updated regularly, as a beginner i didnt have difficulty setting it up, has decent documentation for integrations.
I have a similar tv box running on rk3328. You'll need to flash the rom and put armbian on it. Search by model and you'll find some guide on armbian forums. Mine had 4gb ram but uses only about 600mb running my hubzilla server on docker. And 30gh storage is decent for small projects.
@whoareu cloudflare tunnel can easily help you do that. the only limitation is your domain will need to be from cloudflare. It works well, I am hosting an instance without any public IP and without exposing any ports.
If not a Pi, try to go for those (used)mini PCs, they will allow you a bit more power than a Pi and cost just about the same. Then get docker on it and you're all set for easy deployments.
And look up homelab youtubers, they have some good tutorials for beginners. thats where i started. Jim's garage would be my recommendation, especially his older videos about hardware, security and networking basics. You will need to learn these to keep things secure.
have you tried hubzilla? its multipurpose.