Hey there @Rozza
Option 2 with a custom list because you CAN create a select/deselect all function.
Here’s how:
On the modal screen, add a hidden input and call it “select all input”, set this as a number type input, then set the default value to 0.
Drop a countdown timer into your custom list and make it really small (and/or invisible by setting the color values to transparent). Set the countdown timer to only visible when “Select all input” is equal to 1. Set the action on the countdown timer to update the item add it to the selected options.
Add your “select all” option to the list. When “select all” is clicked, have that change the input value of the select all input to 1. This will then have all of the list items update.
You can add another action to the countdown timer to set the “select all input” back to 0. Set a condition for this action where list items count is equal to selected items count.