KeyCreator / Modify / Fillet / Fillet and Trim

KeyCreator Pro Modify Fillet  Arc

Use the Fillet Arc function to create a trimmed fillet arc.
 

Quick Trim enabled
Cursor position and zoom out to get within cursor radius selection range when entities are not intersecting:

KeyCreator Modify Fillet Arc example
 

Single Select when intersection unclear:
KeyCreator Modify Fillet Arc example 2