Easier than you might think
My podcasts app (iCatcher! Podcast Player on the App Store (apple.com) has an apple watch companion app and at different times you could play audio through the watch speaker for items downloaded to the watch.
In recent years that ability seems to have disappeared. I did some tinkering last year (2020 or was it 2019 🤔) I figured it out.
Simple enough, user has the allow speaker option enabled in the app and the current audio output is the speaker, then set the audio category to movie playback and default policy. Otherwise spoken audio and long form audio.
