I read that as you not wanting to run your own server. If I read that correctly then unfortunately the answer is no, you can’t run on the Anvil hosted runtime and guarantee they won’t update it in the background (ie there is no LTS option).
I don’t imagine it would be cost effective for them to do so, but you could add it as a feature request.
@jshaffstall’s suggestion of your own server is not as hard as all that to set up. There are plenty of instructions, and people on the forum will help where they can if you get stuck.
Also, I believe there is a docker container for it, and you can create a Digital Ocean droplet with docker preinstalled (Docker | DigitalOcean Marketplace 1-Click App) to make it even easier.