Issue with page "bindings/cplusplus.html"

The GStreamer API C++ bindings are actively developed and based on gtkmm, using the same lifecycle mechanism.

It's a lie. GStreamer API C++ bindings are not actively developed, the last update was in December 2018. gstreamermm has problems, for example, it increments the ref counter on in-parameters, which causes calls like gst_element_query to fail, and with GTK4 it won't even compile.