If you don't know Ruby, and you don't know Ruby on Rails, you have 2ish choices:
1. Go with what you and your team already know (unless what you know doesn't apply to the target space)
2. Learn Ruby and especially Ruby on Rails first. Otherwise, you'll end up with a dumpster fire. Make sure you investigate the idioms, and use Rubocop, ruby-lsp, and ruby-lsp-rails -- there are more tools for linting your code that help you learn what not to do.
If you aren't using Rails for the FE, you are losing at least 30% of the benefits, unless your FE is just rendering what Rails is returning and not managing complex state.
1. Go with what you and your team already know (unless what you know doesn't apply to the target space)
2. Learn Ruby and especially Ruby on Rails first. Otherwise, you'll end up with a dumpster fire. Make sure you investigate the idioms, and use Rubocop, ruby-lsp, and ruby-lsp-rails -- there are more tools for linting your code that help you learn what not to do.
If you aren't using Rails for the FE, you are losing at least 30% of the benefits, unless your FE is just rendering what Rails is returning and not managing complex state.