I have been using Samsung phones for a very long time. But after getting the a20e recently, I found that the opacity option was nowhere to be seen. Now correct me if I'm wrong but this should always be an option and I'm sure Samsung don't pick and choose what version of their phones have this option. I care about my eye health and I'm very disappointed at this right now. I have the latest software installed so I'm sure it's not a case of my phone being out of date.
A20e doesn't support this function. Afaik only the below devices have it:
Galaxy S6 (idk but S7 does have it) and above
Galaxy A3 2017 and above
Galaxy A30 and above