@Vlad
words in "quotes" will represent the terminology used for arc
arc's "profiles" are very much linked to "spaces"
there is no real concept of windows in arc (but yes u can create more than one window), as you switch between "spaces"
basically everything is automatically synced and saved. each "space" in arc is equivalent in sorts to a saved window in orion
on the creation of a "profile", you need to choose between ur existing "spaces" and select which one(s) will be linked to that new "profile". all tabs inside those profiles will get moved to that new "profile", meaning cookies ARE LOST.
basically, you could have something like this along the bottom of the sidebar:
there is no way to switch between profiles directly, but instead, you switch between spaces that are linked to profiles