Uncaught TypeError: select.oldChosen is not a function

Seems the library is not installed for the Chosen module. Follow the below step to resolve the JS uncaught issue.

Manual Installation
1. Download the Chosen jQuery plugin.
2. [Drupal 7] Extract the plugin under sites/all/libraries
3. [Drupal 9-10] Extract the plugin under libraries/chosen. Use version 1.5 or higher.
4. Download and enable the module.
5. Configure at Administer > Configuration > User interface > Chosen (requires administer site configuration permission)

Installation via Drush

A Drush command is provided in the latest versions for easy installation of the Chosen plugin.

drush chosenplugin

The command will download the plugin and unpack it in "sites/all/libraries".
It is possible to add another path as an option to the command, but not
recommended unless you know what you are doing.

Thanks I didn't realise the js library was not installed.
I can install chosen via drush
I'm not sure if this operation applies to individual sites or to a whole platform.
The 'chosenplugin' command completes without giving any details.
Because I am installing and running many similar sites on the same platform, I need this operation fully automated, either by a line in the installation profile (if it is required per site) or via composer (it is required per platform)
Can you advise further?
Thanks?

If you are using a Continuous Integration (CI) process to deploy, you can add the drush chosenplugin command there.

For example, in a CI script that connects to Pantheon, we added the following command after config import, before cache-rebuild.

# Move the Chosen Plugin to the correct spot
terminus -n drush  "$TERMINUS_SITE.$TERMINUS_ENV" -- chosenplugin

Now we also have path repository installation.
See 🐛 Chosen 4.x composer installation recommends composer-merge-plugin, switch to path repository instead Fixed