No, per workspace and browser window you can only be logged in with one account at the same time.
In case you do log in with a second account in the same workspace in the same browser but in a new tab, you will need to reload the page where you're logged in with the other account. This will automatically sign you in with the account you logged in with last.
If you do not reload the page in the tab that you logged in with with your first account, you might still be able to open another page (e.g. your profile page), but you will not be able to access projects, change settings, upload a new profile picture, etc.
In case you have any questions or run into related issues, feel free to reach out to use via the messenger.