I have had this nagging issue for a couple of weeks now. After trying everything I tried a different (brand new) cable (both are original apple cables, but the old one I have used for many years and has signs of wear at the connector). With the new cable it stopped asking me to Trust. Plug the old cable in and I get the Trust question again. So the cable seems to be the issue; nothing else has seemed to work. (Mac is an old Mid 2012 Pro on Catalina 10.15.3 and the phone is an 8 with 13.3.1 iOS). I will update if this changes and I develop "trust issues" again, but for now the solution appears to be a new original cable.