Apparently it is not possible to deploy a "classic" SharePoint solution (WSP) to a SharePoint 2016 MinRole server which is running a dedicated search role.
Most likely this is caused by the fact that on a dedicated search server role the „Microsoft SharePoint Foundation Web Application“ service is not installed. (At least I found posts which say this service had to be running in order to deploy WSP solutions. Yet I didn't find an official statement by Microsoft so far.)
Since our solution is a Custom Indexing Connector solution it has to be deployed on the crawl server. This works in most of topologies (in all likelihood as long as the „Microsoft SharePoint Foundation Web Application“ service is running on this server). But in a SharePoint 2016 MinRole deployment, running the crawl server on a dedicated search role is a designated topology.
(As a workaround you can copy the required DLLs manually to the GAC on the crawl server using gacutil.exe. This seems to be working so far but is no really satisfying solution.)
So my question is: is there any clean solution for this scenario?