How to clean the insides of sliding glass door?

A vinegar-water solution (50/50) works great. Spray it on and wipe off with newspaper or a lint free cloth

Are you talking about insulated (double pane) glass that is foggy in between? If so, that means the glass has lost its seal. You can replace with a new double pane, but it can't be fixed otherwise. You could also get a whole new window but more expensive and not always necessary.

Use a long dowel wrapped in paper towels or strips from an old T-shirt. Squirt Windex ITV homemade glass cleaner (ammonia and water) on the covered dowel, and clean away. Sometimes I have used a yardstick when a dowel was too fat ☺️

If you are referring to to sealed double pane glass with gas infused between panes, there is no way to 'clean it'. If it looks foggy or milky, that indicates the seal is broken. Only solution is to replace. There are companys out there that replace the glass only and it's not as expensive as you might think.

vinegar and use newspaper to wipe