1.Icons are only useful for users that already know what they do. Zero value UX wise for new users. Labels matter, especially on mobile where hover is not an option. Having a "walkthrough" on first load is not a replacement. Also, non-native users do not know about hover tooltips, and they will not learn that behavior, they find them almost exclusively by accident.
2.Gradients on mobile, especially with power save, make apps and pages unreadable for everyone, but especially seniors.
3.Hamburgers and triple dots are not visual indicators for non-native mobile users.
4.Swipe is not an replacement for any UX process for non-native mobile users.
5.Canceling/backing out of any workflow is rarely obvious on flat/minimal designs. Seniors click/tap the wrong thing ALOT. Some giant percentage of their time is spent trying to reverse an action.
6.Zoom is king. Non-button looking buttons get even worse if you remove their context. Mouse over only context buttons might as well be invisible.
7.Seniors do not know what blue/purple/green text means. The underline is the only thing my seniors understand. Also, they click pictures, all pictures, because they are the only thing on these apps/pages that actually look like they are clickable.(see number 6 buttons)