I just checked official tor browser, and you can store cookies in it. But, it also gives a warning ‘In permanent private browsing mode, cookies and site data will always be cleared when Tor Browser is closed.’
You can even store passwords, bookmarks, credit cards etc.
The financial websites do not work, not because of cookies but because of your IP address, as you are using TOR Exit node IP, so financial websites flag your session as TOR=Maliciousness.
You can use Facebook, reddit, twitter normally in tor browser. Even some financial sites like crypto exchanges normally via storing cookies.