While you may no longer be able to deduct anything as an employee job expense, I know some musician employees (civilian) who also have some part-time self-employed work, such as side-gig performances, teaching private lessons to students, and other work as an independent contractor. So if you have any self-employment income (1099-MISC, cash, etc.) in your music work as an independent contractor and thus file Schedule C, you may be able to allocate a portion of your instrument's cost to your self-employed work by depreciating a portion of it. Allocating and depreciating can get kinda involved, and I'm not a tax expert, just a fellow user, so I can't help you further with that. I'm merely mentioning it in case you do have any self-employed income from your music work.
ADDENDUM 1/23/20, 8:00 PM Pacific
I found some more info for you. See my next comment below.
