Unfortunately you will have to do this in Code-Editor view and delete the link manually. Looks like a bug to me.
Click on the three dots on the right top of your admin-area and select “Code-Editor”.
You should now see your raw code – now look for your slide-link. If you mess something up here, you will be able to restore to a previous version, so don’t worry.
If you change your link to something unique, you will be able to find it more easy.
Your slide is wrapped inside code like this:
<!-- wp:eedee/block-gutenslide {"background":{"backgroundType":"none","backgroundOverlayImage":"","backgroundOverlayVideo":"","backgroundOverlayOpacity":50,"backgroundGradient":{},"backgroundImage":{},"backgroundPosition":"center center","backgroundRepeat":"no-repeat","backgroundImageSize":"cover","backgroundVideoSize":"cover","customBackgroundColor":"","hasParallax":false,"backgroundFocalPoint":{"x":0.5,"y":0.5},"backgroundVideoFocalPoint":{"x":0.5,"y":0.5},"backgroundVideo":{},"backgroundVideoMuted":true,"backgroundVideoLoop":true,"backgroundVideoAutoplay":true,"openPopover":true},"linkUrl":"https://lala"} -->
Things are seperated with a colon. In the above example you would delete ,"linkUrl":"https://lala"
.
Now save and publish.