@Maximilian Deibert, Thanks for posting in Q&A.
From your description, it seems there is something wrong in your Intune dashboard.
To remove these outdated error messages, please click the error and see which app is failed. After we find the affected app, check the "Device install status" of the affected app to see on which device it is failed. If the assigned users have been removed from the device, please also remove the user's assignment in the app properties.
Could you share with us the applications install behavior and assignment status?
For the win32 apps issue, please check whether the detection rules are configured properly, and we can use Remediation Script to fix this issue.
Here are links to troubleshoot win32 app deployment issue.
https://www.reddit.com/r/Intune/comments/1856sue/clearing_up_old_app_install_errors/
https://www.reddit.com/r/Intune/comments/v6q0z0/can_you_clean_up_the_intune_dashboard_errors/
Non-official, just for reference.
For UPN apps issue, since it downloads apps from Microsoft store, so the error code may relate to proxy, firewall, antivirus, here are some solutions you can refer the fix the issue.
Hope above information can be helpful, if there is any update, feel free to let me know.
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