No "Hollow Knight" boss option for ending the autosplit.

[Influxwafer]

[AlexKnauth]

For most situations, you can just leave out the ending autosplit, and leave "End-triggering autosplit" unchecked, and it's fine. It automatically ends on the transition to the ending cutscene after beating the Hollow Knight.

The "Credits Roll (Event)" autosplit also splits on the transition to the ending cutscene after beating the Hollow Knight, in case you need that as a middle autosplit instead of at the end.

The "Segment practice - THK (Boss)" autosplit also exists, but, as the name implies, it's only meant for segment practice, not for ending runs.