There are almost no hooks left that need to be in .module files.
There are a few things that need investigation:
core/includes/form.inc:955: if (($function = $batch['redirect_callback']) && function_exists($function)) {
core/modules/views/src/Plugin/views/HandlerBase.php:572: if (isset($this->definition['access callback']) && function_exists($this->definition['access callback'])) {
core/modules/views_ui/src/ViewUI.php:341: $cancel_submit = function_exists($form_id . '_cancel') ? $form_id . '_cancel' : [$this, 'standardCancel'];
Active
11.0 🔥
forms system
If I am not mistaken I think for batch we already can use methods as callbacks.
We could explicitly deprecate the procedural option or just let the .module deprecation take care of it and mention how to move them in that CR.
Still need to look at the other two.
Haven't reviewed it yet, but from the title 🌱 [Policy, no patch] Normalize on usage of is_callable() instead of function_exists() Needs review might be enough.