UiPath is adding the @ symbol before String1 because it is interpreting it as a verbatim string literal. A verbatim string literal starts with the @ symbol and it allows you to include special characters, such as new lines or tabs, in a string without having to escape them.
Yes. When UiPath reads a string from an Excel workbook, it reads it as a verbatim string literal by default. This is because Excel allows you to include special characters such as new lines and tabs within a cell, and UiPath needs to be able to preserve those special characters when reading the cell’s value.