I need to check out which ROM my Apple //e and //c have as per [Wayback/Archive] Single Step in Monitor | Applefritter comment by [Wayback/Archive] jeffmazur | Applefritter:
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Apple II: Single Step in Monitor | Applefritter
Posted by jpluimers on 2026/02/10
Posted in //e, 6502, Apple, Apple ][, History, Power User, Retrocomputing | Tagged: 394 | Leave a Comment »
The Wiert Corner - irregular stream of stuff 
Depends upon which machine and ROM version you have.
The original Apple II monitor does have an S command to single step code in the Monitor. That was removed however to add other features and was not restored until ROM00 of the //c. There are however various 3rd-party ROM images that also have the Step and Trace commands, for example ROMeX and ROM4X, APPLEII.EDM, etc.
There are also hardware boards available to do this as well