First I like and use Appimages. One thing that I do find frustrating, unless I am getting blind in my old age and can’t find it. Where is the search function to find an App? It takes ages navigation a list of 1244 and growing items to find one particular entry.
AppImage is designed so that you can get your applications directly from the application author rather than from some centralized store/repository.
Please download AppImages directly from the download page of the respective application, like if you would download the Windows or Mac version.
For example, Ultimaker Cura: Powerful, easy-to-use 3D printing software → “Download for free” → AppImage.