Hello,
This is a long shot but I'll give it a go. I have never developed a custom widget for experience builder and to be very honest don't really know where to start. I have a thing I want to do though, but even if I did know where to start with custom widgets, I'm not sure I would know what to do next.
Get Ireland Active has a really cool activity finder that I want to repurpose for our City's Park Finder app. The main thing I want to take away is that this application uses a custom filter widget where the buttons show a icon as opposed to text, and they are grouped into three major color-coded categories.

I've spoken with someone from the Get Ireland Active team, who let me know that ESRI Ireland built the custom widget for them, but as it was a pay-for-service, ESRI Ireland would not be willing to share the code for it. Very understandable, if a bit disappointing.
So, are you willing to help me reproduce something like this? Is this something that can be deconstructed and rebuilt to some extent? Of course I don't need everything to be identical, but it would be cool to build something similar. I imagine that it's a bit involved for a forum given my lack of experience, so if you are interested, I'm accepting DMs on the topic as well, with the idea that I will post updates and results here.
Also a special thanks to Darragh at Get Ireland Active for taking the time to talk to me about the app and check with ESRI Ireland about it.
Thanks!