I think the description is still not clear. We assumed that by "trailing whitespaces" they mean only the spaces because technically a newline character is ALSO a white space character, but this one we have to keep.
They should be more thorough about which characters they want to keep and which ones they want to strip.

\t is a whitespace and after removing the comment is at the end of the line.

For:

                 v                
Test: String: "\t@ - apples\napples , @\nbananas cherries ! ' =\npears strawberries\ncherries avocados ' lemons" Markers: ['!', '-', '?', '=', '@', '#', '.']`

First you remove the comments, then, you check for trailing whitespaces and remove them:

"\t@ - apples\n" // first line before removing the comment
"\t\n"           // first line after removing the comment
"\n"             // first line after removing the trailing whitespaces

You should remove it only if it is at the end of the line:

Any whitespace at the end of the line should also be stripped out.

Read this: https://www.codewars.com/kata/51c8e37cee245da6b40000bd/discuss#6380f6a2bad8fd6f55799093