In my classes, many students write 'Yes' instead of 'True' on their answer sheet 🙃.
The bad news is: you will be marked wrong.
In the IELTS Reading test, True/False/Not Given questions ask about factual information in the passage, while Yes/No/Not Given questions focus on the writer's opinions or claims. The instructions clearly specify using "YES," "NO," or "NOT GIVEN" for the latter, and examiners expect exact matches—mixing terms like "True" for "Yes" doesn't count as correct.
Abbreviations like "Y" or "N" are accepted for Yes/No/Not Given, but only if the question type matches. Always check the instructions to avoid this mistake, as spelling or format errors can cost marks.