Hey there,
Those API Key / Base URL fields not accepting click or paste on 3.15.x isn’t intended.
Workaround: turn the toggle on, click nearby in Settings → Models, then press Tab until the field is focused - typing and Ctrl+V work after that.
Merging into the main thread: [Regression] Models: OpenAI API Key / Base URL inputs not editable in 3.15.6. I’ll post updates there when there’s news.