When looking at the Tools > Site Health > Info page in WordPress...

• The PHP memory limit value (under Server tab) comes from the memory_limit set in the php.ini file.
• The WP_MAX_MEMORY_LIMIT value (under WordPress Constants tab) also comes from the memory_limit set in the php.ini file when the WP_MAX_MEMORY_LIMIT isn't also defined in the wp-config.php file. ​If the WP_MAX_MEMORY_LIMIT is defined in the wp-config.php file, then this overrides the memory_limit parameter set in the php.ini file.
• The WP_MEMORY_LIMIT value (under WordPress Constants tab) comes from the WP_MEMORY_LIMIT defined in the wp-config.php file (this is hard-coded). If not defined, it defaults to 40M.

I would recommend increasing WP_MEMORY_LIMIT closer to the overall app memory limit by adding something like this to your wp-config.php file: define( 'WP_MEMORY_LIMIT', '2G' ); for a 2 GB memory limit to WordPress for example.

I had found it confusing earlier as to where each parameter was defined and how it was set (and what the defaults are). Hopefully this helps others for the future too.