I just have a question regarding the necessity of ghusl in the below situation.

I woke up and got started on my day. my wife was fixing the bed sheets and she said that there is a stain on the sheets on my side of the bed which she believes is sperm which was not there the night before. I don’t recall having a wet dream and when I woke up I didn’t consider that I had one and the signs of ejaculation were not prevalent to me. I now have a doubt as to whether I ejaculated in my sleep or not due to what my wife has said about the sheets.

Is ghusl janabah obligatory on me in the above case?

It is not required if you are not sure that it occurred.