A box to select all options as a filter in “Inline Filters”
Context: For example, I am trying to add multiple payment system types to my resource directory. However, only the first four were available in the drop down menu when I previewed the site. It took me 10 minutes to figure out why only 4 out of around 20 categories were visible when I previewed my site.
Annoying and a “gotcha” if you don’t catch it!
Yep, this should be fixed sooner rather than later. Quality of life kind of thing.
Another big problem is that if you have lots of options (say 20+), it is very tedious to add them one by one. The default behavior should be to add all options and the site admin then should be able to configure the filter to limit it to a number of options.
I agree with you. It would help a lot to have an option like the one that already exists in the forms (when mapping a dropdown type variable) that allows synchronizing the data source options and thus the options would be updated automatically. Currently, there is no way for the filter to be updated without the intervention of someone who has to keep an eye on it, since in case a new category is added to the variable, it has to be added manually.
Below I share an image to clarify what I am talking about:
It would solve the problem you are talking about too. Moving this option from forms to filters would be very useful! 
Hope this comes soon! And thank you to the Softr team!