Google Search Console: My "indexed" and "not-indexed" pages have flipped. I now have more "not-indexed" pages

Question

I've had a few problems on about 30 pages (all have the same format of an article, just the content of the page changes), that appears to be validated, but only 5 of those actually got indexed. All trace of the other pages disappeared and i have no clue what happened. The rest of the pages seem to appear after i sumbit the sitemap again, it gets "crawled not indexed" and than the rest disappear again.

I've no cluse as to why 5 pages would get indexed, and the rest not because it's all the same react component with just the data it fetches that changes.

This has been going on for about a month and it's important that i fix it because the site contains a lot of educational material for students and the finals are coming up soon so I aswell as probably a lot of students would appriciate if the site goes up.

The website is https://umimcesky.cz/

Any help would be greatly appreciated,

Cheers, Dan

Screenshots attached Page view Discovered – currently not indexed