You can keep it, at least for now. Who knows for sure if or when that may ever change. To make sure your app doesn’t update automatically, make sure to go into Google Play, search for the Wyze app, click on the 3 dots at the top right and uncheck the “Enable auto update” option or Google will eventually update the app for you without your consent. If you uncheck autoupdate, it won’t force the update.
If you do ever update to the version 3.0 (whether on accident or because you wanted to try it out or because support said they couldn’t help you unless you updated to the newest version first or whatever) and then want to go back to the ver2.5 app, you will be able to download the APK from APK mirror at the Wyze collection here:
Just make sure to choose a download that is the APK for the ver 2.5 app, not the bundle option. That will restore you back to the ver 2.5 app.
I hope that helps. 
Possibly, though it wouldn’t likely be allowed on the Google Play store as I expect Wyze would report it as a potentially dangerous mimic app that is pretending to be them and might be trying to steal credentials, all assuming there is no copyright violations of their existing app code. However, if you only use Wyze’s cameras, a lot of people do enjoy using Tiny Cam instead of the Wyze app. It even gives free AI detections. Another option some people like is to convert the Wyze camera streams to RTSP and then view the streams in basically any other app they want and use it in any number of programs or apps. You just have to host a conversion program like Docker Wyze Bridge, or Scrypted or Tiny Cam Pro in Server mode to get the RTSP stream from Wyze and then you can do A TON of things with it without having to even open the Wyze app anymore after the initial setup. I personally love doing that.
Anyway, feel free to keep the ver2.5 app. Wyze has not as yet made any public statement about intentions to force the 3.0 app as the new minimum.