Extreme ranking loss after domain change

Hello,

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I've done several domain changes already, but this one, for this project hit hard.

I have no clue but since 4 months the domain is still not visible at all, I lost all the rankings kind of. I did everything - redirects, new adress change in search console, sitemaps integrations in GSC,..

I have no clue what could be the actual reason.
By typing site:domain.com into google, it shows that only 4 pages are indexed, which is according to the GSC not correct.

Where is my error?

Thanks in advance!