Hi @Michael Farber ,
We could check if the certificate of WSUS publishers self-signed is stored in certmgr.msc.
Besides, we could uncheck the option enable third-party software update, and re-sync.
Here is the guide about third-Party Software Updates:
https://www.prajwaldesai.com/sccm-catalogs-for-third-party-software-updates/
Note: the above links are not from MS, and just for your reference.
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