Hi Josef,
Windows 11 requirements are very strict, and the laptop does not have TPM v2 and the Processor is older than 2018, you may not be able to update to it.
That being said, Microsoft is providing two years of extended security support. One year of which is already almost done.
For European regions, it is free of cost:
https://www.microsoft.com/de-de/windows/extended-security-updates?r=1
Additionally, could you share the System Information copy as advised above, I will be able to help you more.
I look forward to hearing from you to get the results of the troubleshooting.