I like to suggest that icon of a folder (before opening the folder) adapts to the number of content. Say if 4 contents or less, larger 2x2 content icon arrangement is displayed where each have larger size. With 3x3 arrangement with small icon it is hard to see what are inside. Most of the time I only put in 4 or less app in a folder.
How Nova Launcher do it is an excellent example, and the main reason I use it, instead of the default One UI.