Button Controller app appears to be "retired". Is that then deprecated? Is there an alternative?
Rule Machine using the Button Device trigger type not the Button type
Any existing automations you have in Button Controller will continue to work (and you could even add new ones, I think). You can't install the app new if you don't already have it. But you don't need to: as mentioned above, Rule Machine with a "Button Device" trigger gives you the same app but with a few extra actions made possible by RM. The Advanced Button Controller app linked to above is also great, but it is a community app and not the "official" replacement for this app and has existed for much longer given that it originally came from ST. (You can try both!)