I can confirm no masks needed at Costco anymore.
Yesterday I did my first "running errands in Boise and stopping downtown for a burger and beer" routine since this started last year. Cabelas made their employees mask up. Half the customers were masked, half weren't. They had a social distancing sign out, but no mask sign. The german store had a sign out that said (paraphrasing) "The Mayor* no longer requires masks. Customers may wear them if they choose, but we will not be enforcing masks in the store." No one in the store, customers or staff, wore masks.
At the brewpub, all the employees were masked up, and most of the customers walked in with masks, then took them off when they sat down. I entered maskless and had no problem. I think I mentioned earlier one of my favorite brewpubs was still enforcing masks because of their crybaby employees, so I'm not visiting them.
*The Boise Mayor would like Boise to be like Portland, and with the demographics in Boise these days, I could see why people were still wearing masks there even with no mandate. At my Costco, in another county, hardly any customers wore masks. "Mask or no mask" seems to be very geographic around here right now.