How do I stop getting emails from Ryanair? In short: you can't. Ryanair is automatically spamming their customers without a functional system to unsubscribe. If you try to unsubscribe, most of the time they are showing you the following error message:

Unable to create a new connection for server 'localhost' on port '8080': the maximum number of authorized connections (100) has been reached.
WEB-530007 Error relaying '/webApp/objecttoprocessing' to URL 'http://localhost:8080/webApp/objecttoprocessing'.

or Gateway 504 error from their web server. If you ever manage to see the page, it claims that

If your email address is registered in our marketing database you will receive an email to the above email address. You must click on the link in the email to confirm your request. This verifies your email and is a security measure to ensure we only process legitimate requests.

And when you do whatever they ask, the email with a link you are supposed to click never arrives.

If you make the mistake of contacting their DPO, Ryanair’s Data Protection Officer, you will get more spam, and on top of that they require you to give them even more data to sell and misuse: "These requests must be accompanied with either current passport or national ID."

This means you will keep receiving the spam you never agreed to receive, nor gave them permission to send, forever. The only solution is to put Ryanair to spam filter, uninstall their app and stop using their services. If you find any other solution, please share it!