Good feedback is specific, private and useful. Anything else is just an opinion with a microphone.

Feedback that fails is usually missing one of three things. Vague leaves the person guessing what to change, public turns it into a performance about their standing, and useless is just your reaction dressed up as advice. Get all three right and people start coming to you for your opinion, which is a rare thing to be.

Run the check before you give any this week. Can they act on it tomorrow, are you saying it where nobody else can hear, is it about the work rather than about them. If one is missing, fix that before you speak.