krileonOk, I've ran every plugin and core CB through some usecases using PHP 7.3 as I know many are eager (as am I!) to upgrade for the great performance improvements (they are noticeable!). Check out my findings below.
So far within core CB it self I have found no issues regarding PHP 7.3 and CBs functionality. This is rather expected since the backwards compatibility changes in PHP 7.3 from 7.2 are quite minimal.
The biggest change is the update from PCRE to PCRE2, which makes REGEXP a bit more strict, but our REGEXP already has this strict behavior in mind so no issues were found there.
The next big change is a continue in a switch statement will throw a warning. This has no impact on core CB, but it did impact 2 plugins: CB Auto Actions and CB Package Builder. Fixed releases for both have already been released. Note it is just a warning so it would not have hurt the behavior of either plugin, but could be annoying if error reporting is enabled.
The issues discussed in this topic appear to have nothing to do with PHP 7.3. So if you're confident your other extensions support PHP 7.3 and CB as well as your installed plugins are completely up to date it is recommended to update to PHP 7.3 (contact your host if unsure how!). If you should find any issues please be sure to report them on our forums so we can fix them as soon as possible.
If you'd like to check out what's new in PHP 7.3 for your self please visit the below link. If you've any custom code it maybe worth reviewing the changes carefully to ensure your code is also compatible.