[Pepe1vo]

If you're already familiar with RoR then it seems quite a sensible choice to me to just go with that. Working in a modern Rails codebase can be insanely productive and is probably a bit more polished and stable than a modern JS/TS codebase (oh you haven't touched your codebase in a few months? Here are 7 major version changes across 3 frameworks none of which are compatible with one another).

For the frontend I highly recommend Svelte as it's dead simple to get started with and the learning curve is quite mellow. If you don't want to mix programming languages in your codebase, SvelteKit is a good option, but it can be quite finicky to setup and to get working according to your tastes if your tastes stray too far from the SvelteKit happy path.