This is the expected behavior as the Trim processor uses the classic definition of whitespaces, not the extended Unicode definition (which includes the dozens of ways there exist to represent spaces).
To remove it, you have to use a Find/Replace with a regular expression
Replace:
\p{Zs}*$
By nothing
This means "any number of characters of the Zs Unicode character class immediately followed by the end of the string ($)". To learn more about Unicode character classes, see https://en.wikipedia.org/wiki/Unicode_character_property