Q.Boxwood Thinning
I’m very concerned about the health of my boxwoods. Any guidance would be greatly appreciated! For many years my boxwoods thrived; however, I fear I may have trimmed them at the wrong time of year in combination with a very tough winter. Currently, many of the outermost branches have very few leaves as well as a yellow tint. I’m hoping that water and proper fertilizer could help revive them. Thank you so much!

You have a beautiful stand of Boxwood!
Yes, I do think your hedge has suffered some winter damage.
I would allow the plants to recover with adequate water.
Here are some great links to help you with recovery and proper pruning.
https://www.gardeningknowhow.com/ornamental/shrubs/boxwood/boxwood-care.htm
https://www.gardeningknowhow.com/ornamental/shrubs/boxwood/trimming-boxwood-bushes.htm
https://www.gardeningknowhow.com/ornamental/shrubs/boxwood/yellow-or-brown-boxwoods.htm