Unfortunately the answer is there’s no way to do that now. Can’t seem to think of any workarounds for now either, except for accounts. You could do that but I imagine it’s a lot of work to switch between two browser instances. (Are you using the desktop app right now?)
Here’s a link to the this feature request: Search in a specific folder, not all of them
Maybe we should consider adding this to the roadmap soon to gather more votes.