I dug deeper into the problem:
* When I open a very small golang-project, eglot interconnects correctly with gopls
* When I open a larger golang-project, eglot fails to communicate with gopls. In fact, it fails to direct gopls to load the project as gopls stays at a very small memory footprint.
When I uninstall go-mode OR find-file-literally *.go and later enable eglot, gopls is correctly "directed" to load the project, because memory consumption is much higher. In this case it also reports back to eglot "loading packages" and "finished loading packages".
Sidenote: However I cannot interact any further with the LS as eglot doens't consider any buffer as managed:
cl-no-applicable-method: No applicable method: eglot--managed-buffers, nil
eldoc error: (jsonrpc-error No current JSON-RPC connection (jsonrpc-error-code . 32603) (jsonrpc-error-message . No current JSON-RPC connection))
mouse-minibuffer-check: Minibuffer window is not active
but I guess this is because the buffer has no mode eglot considers to be supported.
Sidenote2: If I enable go-mode for this buffer (thus triggering eglot-ensure in .emacs) , a second gopls process is spawned yet without communication between eglot and gopls.