We can't, as a rule, know for certain what is behind feather picking. We understand that it has many possible causes from diet to space issues to individual cognitive quirks.
Since you live where it's winter, and winters are sometimes challenging, your flock may indeed be suffering from boredom if they are cooped up a lot. It can't hurt to address that by either finding a way to let them out as often as possible or increase their run space.
As mentioned, pinless peepers are one of the more effective methods to control the picking. There are dietary things you can try such as increasing the protein in the feed the chickens eat. And another is something we've recently started trying - CBD for our feather picking flocks. You're lucky to have cannabis use legal where you live. You might decide to give it a try. Here's the thread I recently made that discusses this.
https://www.backyardchickens.com/th...lly-found-a-cure-for-feather-picking.1651769/ I've had moderate luck with this in my flock.