Custom template selection not available in templatepick.aspx

Hi, the custom template functionality is gone. I can upload my wsp to the solutions gallery but i cannot choose the wsp in templatepick. The Custom tab is not available. Both the site that i saved as a template and the site where i upload the wsp are classic sites without 365 group. I have been doing this for months now, and since the beginning of this year the functionality is gone. In the past, i uploaded the wsp to the solution gallery, i activated it and then it appeared in the custom tab.

The following document explains this functionality, but it's not available anymore.

https://docs.microsoft.com/en-us/sharepoint/dev/general-development/save-download-and-upload-a-sharepoint-site-as-a-template

Please help!