I would consider this a bug. It at least applies to the image selection modal, and the deletion modal.

The deletion modal on macOS is especially jarring, since delete/backspace is a single key. Unintended composite action involving deletion feels very dangerous...

Another situation is when a modal have text boxes. Since ⌥← and ⌥→ are frequently used to navigate word by word, having the underlying tab going backward/forward in the meantime feels really weird...