I can not enable cookies on my ipad

So, to ask again, are you have difficulties with first or third-party cookies?

iPadOS 13/14/15 disable 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.

As already outlined, first party cookies can be still be enabled in settings:

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; there is no “undo” button or “return to default” settings option. Make careful note of settings before you make any changes - as without your own notes, the only way to restore standard settings is a full reset of your iPad.

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 (blocking) mode:

Are you have difficulties with first or third-party cookies - as for iOS/iPadOS13 or later, the latter are intentionally blocked by default?

To enable first-party cookies (and third-party cookies for iOS12 and earlier):

Settings > Safari > [Privacy & Security] Block All Cookies - set to OFF