That was a lot of fun. There were several words I didn't know but was able to figure out and learned something (for example, the adjectival use of "arch"). I know it's like how a joke isn't funny when it's explained, but can you explain the theme to me? I'm feeling really dumb. :) Thanks for the puzzle!
*Class for learning to control a particular emotion (grief)
41A
Battle city in northern France
42A
Ancient kingdom ruled by Augustus
43A
Contract for secretive matters: Abbr.
44A
Lane for carpoolers: Abbr.
45A
Bumbling
49A
*Process that lets you beat the crowds to the ballot box (labor)
54A
Exist
55A
"Should __ worried?"
56A
United Arab ___
58A
Iconic Batman villain
61A
Direction from which an actor might enter ... or a feature of the four starred entries
62A
Freshwater eel
63A
Knowing and mischievous
64A
Peach or pecan
65A
Played
66A
Hire for a show
67A
Longtime senator from West Virginia
Down
1D
Where to find pinball machines
2D
Mideast capital
3D
Severely injured
4D
Cockney greeting
5D
Not acidic
6D
The planets in our solar system, for example
7D
Enforcer in "The Godfather"
8D
___ Lingus
9D
Some HD screens
10D
Where is he?
11D
Nickname for the Caps' captain
12D
Stimpy's cartoon pal
13D
1950s presidential initials
18D
Word after junk or sock
21D
"Come on!"
24D
To fly to Spain?
25D
Man or Skye
26D
Fruity prefix used by Ocean Spray
27D
Word after Near or Far
29D
Kitchen appliance some use as a storage space
33D
Comedian J.B. who voices Frank the Plant in "Harley Quinn"
34D
Artillery burst
35D
Come to a close
36D
"You said it!"
37D
Adults get this too -- stop telling people their skin problems will be solved when they turn 20
38D
Zippo, zilch
39D
"Get your rear in ___!"
40D
Political refugee
44D
Type of vehicle sometimes permitted in the 44-Across lane
46D
Diner
47D
Marilyn Monroe-starring film, "Gentlemen ___ Blondes"
48D
Tried and true
50D
Feudal lord
51D
Prefix meaning "four"
52D
Apple desktops
53D
"Last ___" (2023 Morgan Wallen song that somehow made it to #1 on the Billboard chart?? I'm a country music fan and even I genuinely do not understand how this is possible)