I recently made a tiny utlity app with a single screen, one dropdown and a few lines of text (it makes a single API call to populate the text).
According to my phone it's 25MB.
There's no assets, not even an app icon.
I have no idea what would be taking up more than a few hundred kb, let alone 25MB.
Is it for iOS? Then, it could be the Swift runtime library.
Maybe your compiler isn't pruning dead code?
There are ways to analyze the content of your app so you know exactly what's taking all the space.
Tools can vary depending on what language you used. For example i wrote a small app using flutter and i used the flutter's app size tool.