Girdling root: Should this be cut?

I need some advice. I'm an aspiring arborist and hope to have my certification by the end of next year. That being said, I've mostly worked in a lab for an Ag company and still have some school left and only a couple of years of practical experience with a separate landscape company that doesn't have a certified arborist. (I'm the closest they've got.) So I'm not going to pretend to know it all. I know that generally speaking, girdling roots are bad and should be removed. However, with this particular, tree I'm not certain doing so wouldn't be fatal.

For context, I have a neighbor that has spruce trees planted around his property as a privacy screen. The trees are around 30 years old at my best guess and are generally healthy looking trees save typical die off/needle drop inside the canopy close to the trunk most likely from lack of maintenance limiting sunlight penetration and air flow. No obvious signs of fungal disease, blight, or cankers. However, many have begun to show signs of stress and I informed my neighbor it's likely from the excessive soil pushed up around the trunks. (Think mulch volcano, but with soil.)

Fast forward to this weekend and I'm helping my neighbor excavate the root collars on all of his trees. Sure enough, most all are dealing with some degree of root girdling above the main root zone–some more severe than others. I know early spring would have been a more preferable time to do this, but since many were showing signs of stress we remedied all but one tree and this is the tree I'm asking for help with.

This one tree has one large primary root that's grown tangentially and more or less seems to have merged with another primary root. It was also 1 of 3 out of about 20 trees that wasn't showing signs of stress, and also lacked secondary roots girdling above the primary root zone. My concern is if left alone, it will eventually choke the trunk or the other root it has run into, killing the tree. On the other hand if removed, I'm not sure it can be done without harming the other root, inflicting more trauma than it can recover from, or compromising the stability of the tree as it's the only major root on the windward side. Should we attempt to remove this root now or wait until spring? Or should we not attempt it at all and leave it be until nature takes its course?

Thanks.