I'm having a minor issue which about to turn into major issue while using Photoshop 2020.
As a textile designer, I mostly use Define Pattern and Pattern contents on fill tool and I'm trying to reset the custom pattern panel into default mode which automatically delete my previous custom patterns as usual, or deleting them one by one manually by clicking Delete Pattern in Fill tool.
But after I changed my subscriptions to Photoshop 2020, This Delete pattern shows as gray color which won't let me delete the patterns. I tried everything to solve but no luck.
As you want to delete a pattern in Photoshop, Select the pattern you want to delete, and choose Delete Pattern from the Patterns panel menu. You can access the Pattern panel by going to Window > Pattern.
I am not sure which tool you are reffering, can you provide more explanation of fill tool or screenshot with problem?
I am testing Photoshop 2020 on Windows and everything work fine. You can delete patterns in Edit > Fill dialogue if that is what you mean by Fill tool. Right click on pattern thumbnail and choose Delete Pattern. As already mentioned, Window > Patterns panel is much better and more convenient way for any task with pattern management including to delete them or to restore to defaults.