Trim commands works perfectly when it comes to bisecting or crossing lines...
But it is not working when it has more than two INTERSECTING curves / line / profile / circle.
What should have been done = If selecting to TRIM line 1,3, and Outer Circle (in actual case, 1,2, and 3 are SINGLE, line) only line 2 should have been TRIM.
What is actually have been done = As per above statement, by selecting circle and line (actually all segments are single), either line 1 or line 3 is deleting, instead of line 2
To make a story short, WHEN I ENTER 'TRIM' COMMAND, RED COLOR LINE SHOULD BE TRIM FOLLOWED BY SELECTING THE LINE OF OUTSIDE OF THE CIRCLE
You are right, it is not possible to do this in LibreCAD with Trim in one stroke. Use Divide instead, cut up the line at the section points to the circle, then delete the middle part.
Or, if you insist on using trim, then copy the line and insert it at the same place, so that it is double, then use Trim at both ends.
It is a tool common in other CAD apps to delete a line section between two other entities by one click, which is still missing in LibreCAD. Maybe one day...