I got this warning after a restart.
What's happening here?

How do I stop windows deleting winpm-32.exe

(Malwarebytes should be over-riding defender)

VIRUS TOTAL RESULTS

I don't think you can stop it. You will likely need to restore it from a backup.

There is something weird going on though. I don't know what version of Pegasus Mail you are running but I just submitted winpm-32.exe from both 4.80 and 4.81 beta to VirusTotal and they scanned clean.

I'm running v4.8
Once I'm running malwarebytes as my main anti-virus so I think I'm okay.

Defender seems to be breaking through during rebooting
but malwarebytes takes over shortly thereafter.

Defender is likely running until Malwarebytes starts up and takes over. If you are relying on Malwarebytes then perhaps you should disable the real-time protection in Defender (Windows Security app).

It's concerning that your submission to Virus Total produced the results that you posted but scanned clean for me.

ran scan on pb3 with https://virusscan.jotti.org and it all comes back with NOT Found.

WINPM-32.EXE
Name: WINPM-32.EXE
Size: 3.5MB (3,673,776 bytes)
Type: PE32 executable (GUI) Intel 80386, for MS Windows
First seen: April 25, 2023 at 10:53:41 PM GMT+2
MD5: d6701b58c67d1977070fb6d8f2b9d526
SHA1: 15f9048d269dd1cffb1df97c7c816c6ecbdefcc9
Status: Scan finished. 0/14 scanners reported malware.
Scan taken on: April 25, 2023 at 10:53:43 PM GMT+2

Avast! Antivirus
Apr 25, 2023
Found nothing
BitDefender Antivirus
Apr 25, 2023
Found nothing
ClamAV
Apr 25, 2023
Found nothing
Cyren
Apr 25, 2023
Found nothing
Dr. Web
Apr 25, 2023
Found nothing
MicroWorld eScan
Apr 25, 2023
Found nothing
Fortinet
Apr 25, 2023
Found nothing
F-Secure Anti-Virus
Apr 25, 2023
Found nothing
G DATA
Apr 25, 2023
Found nothing
Ikarus
Apr 25, 2023
Found nothing
K7 AV
Apr 25, 2023
Found nothing
Kaspersky Anti-Virus
Apr 25, 2023
Found nothing
Trend Micro Antivirus
Apr 24, 2023
Found nothing
VBA32
Apr 21, 2023
Found nothing