How can I increase the length of a text field property?
The property fields are unfortunately a fixed value and cannot be sized larger than their defaults.
If you like, you can submit an idea on Communities to propose the ability to expand the field size. An alternative may be to adapt the property field as a conditional custom field that appears whenever you have selected the given category. This would require further development as a customisation effort.
It looks like this topic came up previously in the Communities, there's some information here:
Increase the length of a text field property
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