Divi Theme - Filterable Portfolio Filter Drop Down Modification

We use our divi theme filterable portfolio for a vehicle showcase and would like to alter the standard in line filter buttons to be a standard dropdown menu showing the parent and dropping down to the child categories instead.

Basically I would like my parent categories displaying and then a drop down for the child categories to allow my customers to filter all the videos in the library by style, time or level/ability. The Divi theme does not allow for a nice looking filter menu so need someone to program a plugin or add relevant code.
Screen shot of what the menu looks like right now not even displaying all the categories that are available.

I am not sure what kind of coding is necessary to get this to display right - maybe PHP, CSS, Javascript

the kind of filterable menu I am looking for is show in the following links:

https://www.app.namastream.com/#/simply-doable-yoga/product/1958/recordings

https://yogainternational.com/classes/

I hope you can help, please let me know a description of your solution approach and estimated time/ cost.

Looking forward to working with you.