If you put your plugin in the WP Repository, and
change the version number in the readme.txt file
put the new code in a new 'tags' folder with the version as the folder name
also put the new code in the root of your repository (and I also put it in the 'trunk' folder
and do the SVN Update thing
Then anyone with the plugin installed will get a notice about ...
You can check your .htaccess file. WordPress will check if you have this line:
# Use PHP 7.3 as default
If it's not the latest PHP version (i.e PHP 5.6), even if you are running the latest version on your host, your dashboard will show that warning.