You can indeed ignore this warning, because Plone does not use the tempstorage. It does create a temp storage still, which is no problem. We will probably stop doing that in Plone 6.
Of course, theoretically it could be that you have an add-on or some own code that uses it. But this is not likely.
In your link, this comment from Hanno is helpful in that case:
I remember we ran into problems with tempstorage and sessions in Plone and removed all code that used those way back in 2004. To my understanding these were considered broken ever since in the Plone community and you either used cookies, memcached or later Redis to store session state.