Joomla 3 to 4/5/6 Runbook

Part 1 -- on the Joomla 3 site (source)

1. Install the J3 package via Extensions → Manage → Install → Upload Package File.
2. Open Components → MuRu Migration.
3. Export in this exact order and save each file:
   1. Users tab → Export All (users-….json)
   2. Articles tab → Export All Categories, then All Articles (articles-….zip, includes images)
   3. Menus tab → Export All Site Menus (menus-….json)
   4. Modules tab → Export All (modules-….json)

Part 2 -- on the Joomla 4/5/6 site (target)

1. Install the J4/5/6 package via System → Install → Extensions.
2. Import the files in the same order, ticking Dry run (preview only) first for each file, then unticking it and importing for real.
3. After the last import: set the home page under Menus, review module positions (J3 Protostar positions differ from J4+ Cassiopeia), and clear the Joomla cache (System → Clear Cache).