I think it is always the best to support low possible OS and devices.

Amethyst for example support minimum Android 8.0 (SDK 26)
https://github.com/atrifat/amethyst/blob/3c3571eaf344d76a669b1d7903e1de5800787ffb/app/build.gradle#L14

For device testing, if possible test the app with low performance budget device such as Redmi (Xiaomi) which popular in developing countries (India, Indonesia, etc). If the app can run smoothly in low performance device then it won't be slow in high performance device (Pixel, or any Flagship phone).
 

 It should work on all androids. Will get a xiaomi for testing 

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 Looking forward to Damus Android, Will 🙂 

 Purchased a redmi 10! $250 phone! Not bad. 

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 Oh, nice, that is a good mid entry phone, can be a good minimum test device 👀

Is it Redmi 10 or Redmi Note 10? The price seems quite different from average

https://m.gsmarena.com/xiaomi_redmi_10_2022-price-11357.php

https://m.gsmarena.com/xiaomi_redmi_note_10_5g-price-10768.php 

 Looking forward for your work :)
Tester here with low end device is here too.