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ChromeOS supports Android apps and there is an Android agent. I've not personally tested if it works though.

This was added in GLPI 10. You can hold the ctrl key down when clicking on the column headers to add additional sort levels.

The referenced value is the system default. Each user has their own preferences that can override that setting.
Can you verify that your user has the setting set?

It is currently possible to do this indirectly using SIM cards.
For direct linking, see:

The search option exists. If you open the search option dropdown and search "Description" it shows up as Followups > Description.

There is a plugin for this, but the information isn't the most readable since the historical logs were not meant to be searched, only viewed per asset.

It isn't quite to the point were I want it in the plugin directory, but it should work for what you need. It will add a "Historical" menu item under Administration that will give you a central location to search all of the historical log entries. You should know that you can only enter text to search the old and new values, and the "Search option" column which is the field being changed can only accept the numeric search ID even though it can display the label like "Name" or "Description".

Already planned/in progress :)

The current PR is only closed because the desired spec was different than what I initially made. It is currently being redone and a new PR will be open when ready.

For the global search, the user can add new columns (even from plugins). It is based on their search display preferences (wrench icon on regular search results page). For lists like the Knowledgebase browse tab, the columns are indeed hard coded currently.