puzzle

 ACROSS

  1 Wood or metal fastener

  6 Fluent in sign language, perhaps

 10 Support in crime

 14 Like some whiskey

 15 Qatari ruler

 16 2014-21 "NCIS" city, informally

 17 Peyote and prickly pear

 18 Dig, as for ore

 19 Birthday candle counts

 20 Words after a major misfortune (in this answer, notice letters 4 to 7)

 23 Grudgingly accept, as a loss

 24 Signal ___ (retweet, say)

 25 Playing music you've never practiced (... 5 to 9)

 31 "Yes, that makes sense"

 32 Deceitful statement

 33 Part of a pub's array

 36 "___ Fly Now" ("Rocky" theme)

 37 Sunbeam

 38 Cello opening

 40 Org. with air quality data

 41 Damage a bit

 42 Not as relaxed

 43 It might uncovers a problem with this clue (... 5 to 9)

 46 Action figure based on a movie, e.g.

 48 Performer's signal

 49 Walk for exercise, or a theme hint

 55 Cats' rests

 56 Prefix for "mobile"

 57 Luminous qualities

 59 Small part of a big lot

 60 Literary king played by Glenda Jackson

 61 Andean camelid

 62 Son of Odin

 63 Key figures at the IRS?

 64 Pondered

DOWN

  1 (Someone else's mistake)

  2 Where something disagreeable sticks

  3 Like the 1%

  4 Spanish for "this"

  5 Drink brewed from young leaves

  6 Put in a worse position?

  7 Issue forth

  8 "___ No Sunshine" (Bill Withers hit)

  9 Giveaway

 10 Like a mechanical watch

 11 Not legit

 12 Word on campaign signs

 13 Assignment

 21 More cooked than raw

 22 Rejection in Reims

 25 Colorfully named herb

 26 Flapjack chain

 27 Commerce Secretary Raimondo

 28 TV channel for consumers

 29 Heightened fear

 30 Handyperson's letters

 33 Typical swag bag

 34 Baldwin or Guinness

 35 Fringe benefit

 37 Aries in astrology

 38 (I can't believe I did that!)

 39 "What's that?"

 41 Troubleshooting aids

 42 T, on a test

 43 Hot spot in Iceland

 44 ___ de Janeiro

 45 Baldwin and Guinness

 46 Hold a class

 47 SysOps admin, say

 49 Insect in a cloud

 50 Wishes undone

 51 Obsessive fan

 52 Takei's "Star Trek" role

 53 Certain nest eggs, briefly

 54 Word after "given" or "trade"

 58 Sorrowful

solution