notes app disappeared from google play store and from phone

what phone do you have? check your apps in the play store, under "My Apps". it should list all of your app purchases.

 

Unless the app was removed from the Play Store by Google, in which case it may no longer be visible in "my apps" (a part of the Play Store that Google have, annoyingly, made harder to find in the Play Store app).

The reason I mention this is that the developer simply discontinuing an app doesn't remove it from your phone. Google can uninstall an app from your phone, but they don't do it often (I suspect that they don't like to remind people how much control they have). In fact Google routinely remove malicious apps from the Play Store without using this ability to remotely uninstall them, so if this is the reason you can no longer find it on your phone then there must have been a serious problem with the app (<cynic>like a copyright violation which annoyed a corporation, rather than just malware that harmed the users<\cynic>).

As to how you can find your notes, that really depends on what the app was and where it stored them as well as why it has disappeared. If it only stored them on your device and its data were removed when it was uninstalled (however that happened) then unless you have a backup it's likely that is that. If they are stored in a folder in the user-visible part of the internal storage (/sdcard) then they should still be there, and if you can find the app elsewhere (e.g. apkmirror or apkpure) and install it you should be able to access them again (if they are stored as plain text you may not even need to find the app). If they were stored in "the cloud" then it will depend on whose cloud they are stored in.

To be honest, all apps have a finite lifetime, and none make any promises for what happens to your data if they close down (or are closed down). So my first rule for anything important is to have a backup, and have it in a format that doesn't require that app in order to read it.

 

You could try using different notes apps, as others may be able to read your old notes.

Of couse, this only works if the notes were stored as files, and not part of the notes app data.

https://f-droid.org/en/packages/com.simplemobiletools.notes.pro/

 

Also, look for your old notes app on other appstores.
Google is not the only source for apps.

https://en.uptodown.com/

 

https://en.uptodown.com/android/search