Having just upgraded a site to 5.47.2 and noting that PHP 7.4 is recommended I rashly took this seriously :) and ended up with 3 messages that splat themselves over the top of the majority of screensm making it unusable. Here's one: "Deprecated: Array and string offset access syntax with curly braces is deprecated in /home/dcmadmin/public_html/sites/default/files/civicrm/ext/org.civicrm.flexmailer/flexmailer.civix.php on line 246" So I'm back with PHP 7.3 as I couldn't find a way to suppress them. So can these messages be supressed? This is a Drupal 7 install with error logging set to 'None' which obviously doesn't include these.
For the flexmailer one, note that flexmailer is now a core extension so you shouldn't have that copy in sites/default/files since it's outdated.
For other warnings, it's pretty much just extensions that have that curly braces warning now. Any extension that hasn't updated its
*.civix.php files yet.