Ah yeah, I generally just switch between US and US-Intl when I need to move to French. Since you can do it with Win+Space, it's pretty convenient, though I do sometimes trigger it on accident.

I don't use windows often enough to have gotten the hang of how it handles layout switching. I think, by default, it's supposed to handle them "per app". Which, in my case, sounds great: I need French for Outlook / Teams, and English everywhere else. Somehow I always seemed to type expecting the wrong layout. So I've looked for a way to have a single one which works everywhere.

Windows doesn't natively support the Mac behavior. I had to find some layout that almost does it, with the caveat that it uses alt-gr instead of mac's alt, which isn't exactly the same nor in the same spot. So I had to pile another utility on top that modifies the WIN/Menu keys to send alt-gr. Luckily, it was also able to move win to caps. So now, aside from the "weird" altgr, I'm happy enough with my keyboard under windows.