"Hi, is there any way or function to define the encoding format of an external text file during import, specifically to differentiate between UTF-8 and ANSI?"

I only know of an "unofficial" way. Sometimes there’s some header bytes added to mark UTF files. Wikipedia has some collected information:
https://en.wikipedia.org/wiki/List_of_file_signatures
https://en.wikipedia.org/wiki/Byte_order_mark

But it is not guaranteed that a software creating UTF files uses such header bytes.