How do I stay logged in on Safari 12?

Since upgrading to Safari 12, many sites that I could remain logged into for extended periods of time now aggressively log me out, often several times a day. Sometimes it even becomes difficult to successfully log back in again.

Sites where I have this issue include Amazon (both the store and AWS), SE sites, G Suite, Facebook, GitHub, and many other major sites. Typically logging in again requires reentering two-factor authentication, even if this has been disabled for Safari (with "don't ask again", or "trust"). Other sites (e.g., Wikipedia, The Guardian) have no trouble keeping me logged in, even with ad blockers fully enabled.

My Safari privacy settings are:

How do I stay logged in on Safari 12? What's changed or what do I need to change to get the old behavior back?

Solution 1:

Update: macOS Catalina has resolved the issue for me.

The only workaround as of now is to use Safari Technology Preview. If you delete all Safari folders from your home directory, you can stay logged in to the first few websites you visit. After this initial period, it starts deleting cookies for all future websites.