Hard to say, maybe cork? Does it feel somewhat resilient or hard? Could also be an older version of OSB.

It’s hard and smooth. I’m concerned about asbestos. I think I will tile right above jt

It's either rubber flooring or real linoleum. You'd have to remove a small piece to determine. Linoleum will have a jute back where rubber would be homogeneous and glued directly to the substrate.

Have someone come and look at it, and get exactly what it is. These are all guesses. My guess, is because it is upstrairs, there wasnt any hardwood there, and that is an older version of osb sub flooring. However, these are all just guessing, Have a contractor look at it, and tell you for sure.