Should I switch stacks/orgs if that could delay my promotion?

For context: I’ve been working as a Frontend Engineer for 10+ years, I consider myself a skilled engineer and I’m on a solid path to a promotion from Senior to Staff (1 meet expectation / 1 exceeding / 1 defining new standards)…but I’m getting tired of “just” doing FE / I’m in my comfort zone when it comes to my day to day job; I still enjoy the work I’m doing and I also do a bunch of glue work (work x-fn, mentor others lead initiatives, interview candidates)

I have the chance to switch orgs and start working as a Fullstack and then transition to a BE position later, and that excites me a lot, I’ve been wanting to do that for quite a while. Thing is, I won’t be able to perform at the same level I’m performing right now because I’ve never worked on the stack we use for the backend (I do have experience doing backend work here and there with Node/PHP, but I’ve never worked as a BE professionally), therefore I will be taking “a step back” in terms of getting a promotion, to me it sounds unrealistic to perform at peak senior level if I’m making the switch, and this will delay my promotion probably 6-12 months (from my pov). This new org has a good and supporting manager and some exciting projects to work on.

So, I’m debating between a “clear” path to promotion to Staff (with a pay raise) vs switching stacks/orgs and probably delay my promo for another year (assuming things go smoothly) -> and probably not getting a pay raise, or not as significant as the one I’d get from Sr->Staff.

Thoughts? I’m leaning towards switching orgs because that will make me a better engineer AND means more job opportunities in the future (from my pov). As a personal note I also think that the market for FEs has shrinked dramatically in the last couple of years. But I’d love to hear your thoughts!!