GCC 14 educates us:
In file included from ../libs/ardour/ardour/io.h:44,
from ../libs/ardour/ardour/route.h:50,
from ../libs/ardour/ardour/session.h:92,
from ../libs/ctrl-interface/midi_surface/midi_surface.cc:30:
../libs/ardour/ardour/port_set.h:92:37: warning: template-id not allowed for constructor in C++20 [-Wtemplate-id-cdtor]
92 | iterator_base<PS,P>(PS& list, DataType type, size_t index)
| ^~
../libs/ardour/ardour/port_set.h:92:37: note: remove the ‘< >’