Dropdown multiple checkboxes filters

Hello comunity! I need your help today.
I need a multiple checkboxes filters but like a dropdown ( similar with that in the bottom photo) to filters a database in which i add some boolean .

The example is from this site : https://a2bikes.co.uk/browse
And i really need the help, i saw some examples but is not what i m looking for or i dont know to add it to my site.
I am new at this and i dont know javascript or to add same plug-in .
(If somebody contact me , please give me a email to speak or somethink, i dont know why is not working the messages on forum)

Thanks so much !

Multi-Select Dropdown
Create a dropdown menu with checkboxes and search a database using multiple filters.

I saw this, but i dont need that because on this filter the checkboxes are allready selected, i want to let people select what checkboxes they want and if no checkboxes is selected, all items need to be listed.