JJ1992
There has been a upstream change to chromium that vanadium inherits.
You can change the behavior for handling of first party cookies for all sites or individual sites in Settings, Site Settings, On-device site data.
Can delete this site data quickly for a given site at any point from its site info screen or from Settings, Privacy and Security, Clear Browsing data
Can alternatively use incognito tabs and then this data is automatically deleted when vanadium is closed. Can quickly close vanadium by swiping it away from the recent apps screen.
To make easier use of incognito tabs you can enable the Open external links incognito option in Privacy and security settings so that all websites opened from other apps are in incognito tabs. Can also long press on the icon to launch vanadium and drag the incognito tab launcher onto your home screen.