In ArcMap when you are viewing data in the List By Selection mode there are two buttons, one for toggling the ability to select the other to clear any existing selection, as shown below:
In ArcPro I prefer the check box approach to toggle on/off select-ability but it really is frustrating that there is no equivalent clear selection on layer button as in ArcMap. In ArcPro I have to right click on the layer > selection > clear selection. That is essentially 3 clicks when ArcMap had a really useful button...zap done!
This has been marked by Kory Kramer as a Duplicate of https://community.esri.com/ideas/13744-deselect-features-from-table-of-contents-selection-tab-in-arcpro Please visit that idea to vote and comment! Thank you!