So there are tools that autoformat as you type?

let longVariableName = "hello " + this.name;

magically becomes

const longVariableName = `hello ${this.name}`;

without visually flagging it, just autocorrects as I type?

And... I can just quickly swap settings for different clients? Because one has eslint block any PRs that don't have "prefer template" rules followed but another client doesn't like that style, and don't want that style in their code because it conflicts with existing style.

I don't think that counts as a formatting issue. Yes, if your clients have hard rules about different coding styles at that level then it's not a technology problem (nor is it likely solvable with technology). I assumed we were talking about formatting issues like tabs-vs-spaces, in which case yes every single project could be different but auto-fixed.

thx. sorry, i sounded a bit snarky before and wasn't meaning to be. it's just easier for people to focus on visual issues vs operational/functionality. and switching between multiple projects/clients/standards illustrates to me how relatively unimportant some of these things are (but of course just imo).

I would encourage you should check out editorconfig more closely. The whole idea is that each project has a file that defines the simple formatting rules for various file types in the project/directory tree and your editor will automatically follow them on a per-project basis. It's surprisingly well supported across editors.