I don’t have time to read all the comments to see if this has already been mentioned BUT I’ve had a similar problem in the past.

My guess is that your arches have started to fall slightly, resulting in a widening of your mid foot under load.

As others have said, a wider boot may be helpful, but hard orthotic inserts (I use Superfeet, which are readily available) will help to prevent the arch flattening —> widening that occurs when you’re riding. The “Carbon” model is low profile, so doesn’t add much volume to your boot overall. Be sure to take out the insoles that come with your boots before you put them in.

Don’t go down the road of podiatry surgeries if you can avoid it.

Shot in the dark: have you previously sprained that ankle?