Hi! There is a dedicated clause in the service’s terms of use allowing the use of these imagery layers for OSM: “The Service and its contents can be used for the following purposes: […] Production of Open Data derived products”.
These seem to be different sites.
The orthophoto it published at maps.civis.bz.it
The permissive terms are for geoportal.buergernetz.bz.it in general. When searching for the term “orthophoto” on geoportal.buergernetz.bz.it, the list shows a 2023 orthophoto with a CC BY 4.0 license statement
The application on maps.civis.bz.it is just a web-gis to visualize various data sets and maps which come from different sources (many come from geoportal.buergernetz.bz.it, but there’s also some stuff from other agencies of the province’s administration, OSM, etc.).
As the orthophotos are released on the geoportal, their terms of use apply. And, yes, the imagery is additionally also available under CC-BY 4.0, e.g. for when one wants to use it directly on a map or similar use cases.
PS: The above mentioned clause was added to the province’s “GIS service” terms of use many years ago specifically to allow its usage for mapping in OSM. This was even long before the current geoportal existed and none of the (orthophoto) layers had been released as open data.