It's a UTF-8 BOM: Byte order mark - Wikipedia
You can open it in an IDE or editor like VS Code and save it with a different encoding (e.g. UTF-8 without BOM): https://code.visualstudio.com/docs/editor/codebasics#_file-encoding-support
Edit: In the Arduino IDE 2.0, you can use Ctrl+Shift+P Editor: Change File Encoding Save with Encoding UTF-8.