I think this is a good time for a shameless plug. The last 2 month or so I am working on my own project [1] for learning more characters. I have made a tool with powerful search function, training mode, and other useful features, such as displaying plots that show you your progress and whether you are reaching your daily training goal, and the ability to save searches, a la Thunderbird saved filters. It is written in Python and oldschool tkinter with custom widgets for a somewhat more modern and capable feel. It is very configurable. Though currently configuring it means touching a JSON file, as I have not yet bothered writing GUI for that.

I am mostly developing this for myself, to have the perfect tool for me, but I dare say, that I have not seen anything comparable and that I let my 10y+ experience in learning Chinese influence my design decisions. Oh, and it is free /libre software of course (AGPL). It comes with an ever improving vocabulary file that has tons of metadata about words, their usage, how to memorize them, etc. under ODbL (open database license).

[1]: https://codeberg.org/ZelphirKaltstahl/xiaolong-dictionary