Your understanding is correct, however it might not be the case regarding your understanding regarding where to find the jmeter.log file.
If you're running JMeter from it's "bin" folder - the jmeter.log file will be generated/updated in this folder
If you're running JMeter from another folder, it will be generated in that folder. If this is your case - instead of looking for updated log under M:\Apps\apache-jmeter-5.2.1\bin
look for in in %cd%\jmeter.log
If the above hints don't help - most probably your log4j2.xml file got corrupted somewhere somehow, get the brand new version from JMeter GitHub
If you want JMeter to store the log under M:\Apps\apache-jmeter-5.2.1\bin
folder no matter where you run it from - replace this line:
<File name="jmeter-log" fileName="${sys:jmeter.logfile:-jmeter.log}" append="false">
with this one:
<File name="jmeter-log" fileName="M:/Apps/apache-jmeter-5.2.1/bin/jmeter.log}" append="false">
and on next start of JMeter you will see the "log update" you're looking for.
More information: How to Configure JMeter Logging
Also be aware that according to JMeter Best Practices you should always be using the latest version of JMeter so it might be a good idea to perform an upgrade