App Login - 401 error

[J-a-k-o-b]

Hi,
for one customer i´ve planned to handle data in the user onedrives based on a automatically started script. Because we´ve disabled basic auth, I have to use modern auth to get this task done.
I´ve created an App Registration in the AAD and assigned the Permission "Sites.FullControl.All" to the App, and granted consent. Then i´ve created a certificate and used it for the login. I loop through all onedrive urls which i want to handle in that cohort, and log in to the related site:
connect-PNPOnline -Url $PersonalOneDriveURL -ClientID $ClientID -Thumbprint $CertThumbprint -Tenant $TenantName
The connect is finished without any error, but if i want to read out the libraries for example by using get-pnplist i get a 401:

If i check the token:_

the role looks right.
In another environment where i use the same methods to connect and do stuff, i don´t experience a error. I´ve already reviewed the SignIn, ConditionalAccess and Audit logs but without any finding.
Any idea what could be wrong here?