Deprecations are annoying when you first see them in a test run, but they are also one of the best upgrade tools PHP gives us. PHP 8.5 is a good example: the useful thing is not the warning itself, it is the checklist it creates before PHP 9 turns some of this into real breakage.
The PHP 8.5 change list on PHP.Watch includes deprecations for non-canonical scalar casts like boolean and integer, old aliases such as mysqli_execute, no-op cleanup functions including curl_close, curl_share_close, and xml_parser_free, plus a few older constants and output-buffer behaviours. None of that is glamorous work.
That is exactly why it is worth doing early. These are the changes that tend to sit in forgotten corners: old helper libraries, vendor-adjacent glue, migration scripts, and code that has not been touched because it has not failed yet. A deprecation warning gives you a cheap way to find those places while the application still runs.
I would treat PHP 8.5 deprecations as maintenance work, not release noise. Run the test suite with warnings visible, clean the simple replacements first, and write down the bits that need more care. It is less exciting than arguing about syntax online, but it is also much more likely to save your afternoon later.