Migrating Joomla 3.X to 4.X with Installatron
Joomla 3 no longer receives (security) updates
Installatron reports that you have the latest version, and that is correct: 3.10.12 is the final release of the Joomla 3 line. However, moving to Joomla 4, 5 or 6 is not a regular update but a migration, which is why it is not behind Installatron's update button.
Two things to know first
Do not raise the PHP version yet. Joomla 3.10 does not run on PHP 8.1 or higher; your site will break immediately. The right order is: migrate Joomla first, and only then raise the PHP version.
Your template and some extensions are the real work. Your current template was built for Joomla 3 and does not work on newer versions. The same applies to various plugins, such as the Nextend 2 slider. Every migration route therefore involves a new template and setting up sliders and galleries again. Smart Slider 3 and Akeeba Backup do have modern versions.
Two possible routes
Route A: rebuild from scratch (our advice for a small site). Use Installatron to install a fresh copy of the latest Joomla in a test location (for example a subfolder or subdomain). Choose a modern template there, move the articles and menus across and rebuild the sliders and galleries. This new installation runs on a current PHP version straight away. If you are happy with everything, put the new site live and remove the old one. Advantage: your current site simply keeps running in the meantime and you do not carry over any outdated leftovers.
Route B: migrate in steps (the official route). First make a full backup (with Akeeba or via Installatron). Then run the "Pre-Update Check" in Joomla 3.10, migrate to Joomla 4.4 and then move on to the latest version. Finally, raise the PHP version. Please note: your template and extensions need new versions for this. If they do not have them, this route will also require a new template and rebuilding parts of the site. This route mainly makes sense if you want to keep a lot of content or user accounts.
Important: always make a copy of your website in Installatron before you start.