I've switched to Zen browser recently (I like it's spaces and folder structure to organize work on a daily basis, same as Arc). fFox nightly is not there yet but it's getting close with tabs on the left..
Actually you can do it in chrome (having multiple profiles basically), but yeah nowhere as good as arc is, i'm using zen rn but still very sad for arc, I have some hopes they bring back arc to life (either directly or inside of Dia)
I think the one you replied to was referring the fact that Arc can have multiple windows (terminal) "attach" to same tab (tmux session), that has nothing to do with profile.