The SCITE editor that the MAXScript editor is built on supports autocomplete, which you can enable for recognized MAXScript.

3ds Max generates an API keyword list automatically to support MAXScript autocomplete. In previous versions, users need to generate this list themselves, save it to a file, and add an entry for it in the MAXScript Editor configuration file. Available in 3ds Max 2020.1 Update and higher.

The configuration for autocomplete is located in the MAXScript Editor and MAXScript properties files.

In MXS_Editor.properties:

#autocomplete
autocompleteword.automatic=1
autocomplete.choose.single=0

In MAXScript.properties:

#autocomplete
autocomplete.MAXScript.ignorecase=1
autocomplete.MAXScript.start.characters=$(chars.alpha)$(chars.numeric)_#.
autocomplete.MAXScript.useautogeneratedapi=1

To disable autocomplete, change autocomplete.MAXScript.useautogeneratedapi to 0.

You can generate the API list yourself using the generateAPIList() function:

ss = stringstream ""
generateAPIList ss

For more information about these and other properties, see MaxScript Editor Properties File Settings and MAXScript-Specific Language Settings.