Cookies

iOS/iPadOS 13-16 disables third-party cookies by design, using ITP (Intelligent Tracking Protection) - this being a significant enhanced privacy feature of the OS.

You’ll usually find that older sites, that still force third party cookies, will be automatically blocked - but you’ll often find that you’ll have a click-through option that allows you to enable cookies for the webpage for the duration of the session.

First party cookies can be still be enabled in settings by disabling Block All Cookies.

If you known what you’re doing - and still wish to disable the privacy protection offered by ITP and third-party cookie blocking - you can do so from Safari Advanced settings. Be aware that you change any of these settings at your own risk.

The setting that you need to change works in reverse logic:

Settings > Safari > Advanced > Experimental Settings > Disable Full 3rd-Party Cookie Blocking (ITP) - set to ON

The setting is shown here in its default/safe (blocking) mode: