We're about to need to do the same thing with similarly sized codebase. Would love to hear your story. Did you find any migration tooling to help? Would be happy to DM to chat as well.
One of our issues is that we've used some component frameworks that also need to be migrated.
I did it to a similarly sized codebase too. Vue itself was painless.
I also migrated our component framework, from Buefy to Oruga. Some string replacement to change component prefixes, then Typescript to help catch incorrect properties. I might have fixed several bugs in the process thanks to Typescript working better with Oruga. The only real tricky part was converting customized CSS, which was A LOT in our case, but Oruga provides a better way of overriding CSS, so it was worth the time.
Took about 2 days of me doing pure coding with a blocked calendar, plus a third day for testing and code reviews by the rest of the team.
With the caveat that I don't do software engineering professionally, I recently migrated a personal Vue 1/JavaScript project to Vue 3/TypeScript, and it was mostly painless. There's a migration guide¹, and Phind and Copilot were helpful.
Basically, see other comments. We simply followed the migration guide. Very painless. We use few external libs, så that helped a lot. You can find me on LinkedIn with the same username as here for DM.
One of our issues is that we've used some component frameworks that also need to be migrated.