Tensorflow is required for Rasa Open Source, which is in turn required by Rasa X, but there is some flexibilty with which Rasa Open Source version you use with Rasa X - see the Compatibility Matrix
Rasa Open Source 1.4.4 introduced tensorflow 1.15 as a requirement; Rasa 1.8 onwards supports Tensorflow 2. I’d recommend updating to the latest version of Rasa/Rasa X if possible for your set up, if not, you can use the compatibility matrix to find a combination that works for you. You can also check the Rasa Open Source changleog and search the page for tensorflow to see what changed between releases.