I have been using Whisper to transcribe my audio notes. I just save my voice memo from my phone to my NAS and my little script does the rest on a loop.
If you have an always running server and only need access via a browser, forwarding port 80/443 to a reverse proxy works well. Dynamic DNS can be used if you don't have a static IP address. Alternatively, if you are more security conscious and don't mind the reliance on CloudFlare, you can use CloudFlare tunnel which won't expose ports from you local network at all. It can also be combined with a third party authentication mechanism.