Pro currently does not use standard behaviour when clicking in a setting text box.
Current behaviour:
Click in setting field > Double Click selects digits in front or behind decimal point, or units. No amount of clicking can select all.
Text settings after a double click in various locations in the text box as example:



Expected behaviour:
Double Click on field to select all in the field > type values to set new parameters.

Also see this idea:
https://community.esri.com/t5/arcgis-pro-ideas/when-using-tab-to-jump-between-properties-select/idi-...