I want to overlay a twenty line poem on my photo. How to do this on my 2021 iPad Pro? Thank you.

You could do it by marking up the photo directly in Photos. Open the photo, tap "Edit", tap the Markup icon (the circle with the marker tip in it), tap the plus symbol by the markers shown at the bottom, then tap "Text". Type your poem, select your text color, and position it as desired.

You could also use Pages.

Or you could install any number of photo editing apps if you want more options than those two provide.

Good luck!