Users often wonder about this size issue with Flatpak. That's a total of several packages.
Using "Drawing" as an example, the download size of that program is actually just 5.5 MB (see below). The rest is the gnome runtime needed to support it. When additional Flatpak applications are installed that use that same gnome runtime, the runtime won't be downloaded with them. They all use the one already installed.
Notpad Next is a KDE application, so can't share the gnome runtime. It needs the KDE runtime to be installed, and since you don't have that already, the larger initial total download. By itself, Notepad Next download is only 2.1 MB. That's all you would download if KDE runtime was already installed.
KDE runtime when installed uses 846 MB
Gnome runtime when installed uses 754 MB