The new syntax /execute updated in 1.19.50 will suggest subcommands and selectors as long as you type the correct syntax. However, this command candidate will not be displayed only when you add an item to the selector like @e[type=item], and you cannot perform tab completion etc.

Note that if you enter the correct command, the command will work

(how to reproduce)
1. First enter /execute
2. Typing at or as with special selectors
3. Enter @e[type=item]
4. There are no command suggestions that should be displayed.

(expected result)
When you type /execute as @e[type=item],
Command candidates are displayed and tab completion is possible.