Hi,
No. If it's a text custom field, you can only use a text filter on it.
In that case, the users will see a text input for the filter and it will search among the values entered in the custom field in the products.
If you want a dropdown/radio/checkbox filter, then you need to use a dropdown/radio/checkbox custom field.
The only exception is if in your text custom field, you're entering numbers. In that case, you can enter steps in your dropdown/radio/checkbox filter and the filter will display selectable ranges based on these steps to be able to search among the values in the custom field.
There is no functionality in the works for now to be able to generate the values of a dropdown/radio/checkbox filter from the values entered in a text custom field.
We actually want to redo the filters system from the ground up this year or next year, so we're waiting before implementing new features in that old filter system so that we can directly add them once the new system will be available.