I see Neko brought up a lot, but honestly when I tried it a couple years ago it felt pretty clunky. It seems designed more for anime watch parties than serious security or remote isolation, IMO.
I totally get the Tails/Firefox preference, tho. If you want absolute baremetal isolation on your own hardware and have the discipline for it, a fresh Tails USB is definitely the right move. BrowserBox is just a different architecture -- it's mainly for when you specifically want an ephemeral Chromium setup on ... well ... anything, need some policy controls or programmability. And don't want to fiddle with config yourself.
Ah but I'd want to run it myself anyway. I wouldn't want it hosted. Especially for browsing, I don't want someone else's systems looking over my shoulder.
I avoid cloud stuff as much as possible in my personal life. When you mentioned github actions I thought it was something you could self-host too, I didn't realise it was a service only. I was looking for a docker or something but as it's not free and (less importantly) foss it won't work for me.
And yes neko is not a polished corporate solution, but it works for me as a home user. It's very flexible to build other stuff with. I have several instances here in different environments (and I don't expose them to the clear internet)
But for work yeah I know there's different options, at work we have zscaler remote browser.
As to cloud - indeed, why would you want to trust a cloud provider with sensitive internal browsing? Also, providing a SaaS is a hassle, but I feel I must do it serve that side and enable those uses, some of which are cool.