From a source code perspective, moving is as easy as pushing it to another platform. Everything uses git under the hood.

However, all the project mgmt stuff like issues and PRs and releases aren’t as easy

It makes me feel like when people insist it would take an astronomical amount of effort to move their community off of discord.

I know it will but you are worse than wasting your time putting that decision off because it will limit your community in ways you cannot even perceive yet.

Stop wasting everyone's time, don't build houses on top of destabilized sinking mud and expect people to move in, and if they do now you have a MUCH bigger problem on your hands than the challenge of building a new building since you have to convince people the old building which looks fine is not safe.