Most pavilions run an open call for session proposals in the months before the COP. Find the pavilion whose theme matches your work, find its host, and apply to that call.
The calls are not centralised, which is the whole problem. Each host publishes its own, on its own page, with its own deadline, and most of them close well before the conference. Several for COP31 closed in August and September 2026.
A proposal that lands tends to show a replicable result rather than an institutional update, and names its speakers rather than promising them. The Mediterranean Pavilion, for example, asks for sixty-minute sessions with no more than five people on stage including the moderator.