Can I revert to iOS 17 on iPhone 13?

I have an Apple iPhone 13 which is currently using iOS 18.1.1. However, since installing iOS 18.1.1 I have found out that an important app I need to use to monitor my diabetes is not compatible with this operating system and I need to go back and reinstall iOS 17.5.1 or earlier. Apple Support say there is no way to do this but is there anyone in the Apple Community who knows if this in fact possible and how to reinstall a previous operating system please.

[Re-Titled by Moderator]