Firefox has a setting to automatically delete all cookies on shutdown. You can keep a whitelist of sites that are excluded from this (the ones where you want to stay logged in). Works great, and no more worrying about cookies, as long as you shut down your browser now and then
There's not a lot to track in a single browser session. The privacy violation of tracking cookies is that they track what you're doing. If you set the privacyguides.org recommended settings in Firefox, Mullvad or Brave, the cross-site tracking should be blocked, but deleting them completely means the site will even have to do some advanced fingerprinting to even know "it's you" on the same site (if not using the same public IP, for example by using VPN, otherwise the IP will be recognised)
Thank you for commenting and asking the questions! You're never the only one wondering about these things but someone needs to actually dare to ask instead of just scrolling past!
https://privacyguides.org is an amazing resource, often with links to further explanations of concepts.