I recently ran into this issue and Automations do not currently support formula columns.
There is a relatively simple in-app workaround though. Use the General Caster App - General Caster is here. Get rid of formula columns! - #11 by rob
You should be able to find them in the App Marketplace now but I’ve been using it since open beta.
It’s pretty simple and works similar to the formula column but your results are put into a basic column like Text or Numbers which can then be used by Automations and Integrations.