Ask specific questions

"Any feedback?" almost always gets "no, all good". People need a narrower, safer question. Try: "What is one thing I do that helps the team, and one thing that sometimes gets in the way?" or "In the presentation, what was the least clear part?" or "If you were me, what would you work on next?"

Ask about a specific situation, ask for one thing rather than a full review, and tell them why you are asking. Asking face to face or by voice note often gets more honest answers than a formal form, but an anonymous form can help with groups. Give people time; some will reply days later.