IOS cursor moves to end of word after selecting middle of word

This is the standard text selection behavior on iOS—you can see the same in Apple’s Notes app, for example.

To place the cursor in the middle of a word, tap and hold the word to bring up the text loupe, which lets you position the insertion point precisely.

On iPhone, you can also tap and hold the space bar on the on-screen keyboard and then move your finger to move the insertion point more easily.