Google/Alexa: handle string variable to HA

I want to hand overvstring Variables in voice commands to HA with voice commands.

So I can say

Hey Google / Alexa: Do(x)
which triggers a function Do on my HA with parameter x.
Xs type should be a string.

Which assistant does not matter.

I have read a lot about this topic, but most is outdated.
There has been NodeRed, but apparently it does not do what I want even longer.

Any advice on this?