I think that's the sticking point, declarative toolkits didn't mesh too well with C++(or C) projects so we have a bunch in Rust but that's not too interesting for those with existing codebases, I started on a C++ 20 prototype myself a few years back (because to make it even remotely elegant I felt that I wanted designated initializers from C++20) but it kinda turned into a huge hairball of templates to even approach something like react style jsx/tsx rendering.
I'm pretty sure that something based on IMGui could be more or less isomorphous to React style rendering, it'd be up to someone to implement it though (and it'd probably be worth it since building applications at scale you win back a lot of time by not fiddling with state manually all over the place).
Using Chromium however is explicitly not where we should want to go (it's basically a kitchen sink in itself), but we go there anyhow (me included often) because it's just so much more quick thanks to progress in dev experience in the webdev area.