Dear who who who,
I appreciate, very much, you reached out to me. Thank you for your interview offer. It is good to learn that my capabilities potentially match what you look for.
Even though I started looking, but currently I am tied up with a project for which I have a core function in. I would not like to leave until my core function is performed (approx. in x months) to keep my integrity in my current job. May I keep your contact and offer ready for when I am ready to re-enter the job market? I do intend to move on to a new job in 2021.
Thank you again.
who who who.