Waiting for a reply from MeLabs forum to get the custom programmer working in MCS+5.
Too many threads about the same topic.

I just set up MPLABX 5.35, MCSP5, and installed the PICKit4 as a custom programmer.
The only thing I changed was the commandline parameters
Code:
-TPPK4 -P$target-device$ -F$hex-filename$  -W3.3 -E -M -Y -OL -OB
(TPPK4=use generic tool PK4 instead of 'BUR serial no', W3.3=power target from PK4 @ 3.3V)
Those changes shouldn't matter much.

Here's the output from the commandline window
Code:
*****************************************************
Connecting to MPLAB PICkit 4...
Currently loaded versions:
Application version............00.09.46
Boot version...................01.00.00
Script version.................00.05.58
Script build number............abbfe90327
Tool pack version .............1.15.1688
PICkit 4 is supplying power to the target (3.26 volts).
Target device PIC18F26K22 found.
Device Revision Id  = 0x4
*****************************************************
Erasing...
Erase successful
*****************************************************
Calculating memory ranges for operation...
Erasing...
The following memory area(s) will be programmed:
program memory: start address = 0x0, end address = 0x7f
configuration memory
Programming/Verify complete
 Program Report
05-Apr-2023, 07:07:36
Device Type:PIC18F26K22
Program Succeeded.
PK4 Verify Report
05-Apr-2023, 07:07:36
Device Type:PIC18F26K22
*****************************************************
The following memory area(s) will be verified:
program memory: start address = 0x0, end address = 0xffff
configuration memory
EEData memory
User Id Memory
Verification successful.
Verify Succeeded.

Batch Mode Count : 1
When you select 'Program' in MCSP, the command window opens and it takes a good 10 seconds before anything happens. That's just the way it it with ipecmd and MPLABX.

If you've installed multiple versions of MPLABX, make sure you use the matching versions of ipecmd.exe and MPLABX IPE to test it with.
Also, when you setup the custom programmer entry in MCSP I'd use the "find manually" option for setting the path, which for me was
"D:\Programs\Microchip\MPLABX\v5.35\mplab_platform\ mplab_ipe" since I use custom installs. Be sure to test it using the IPE first... that way you know everythings working.