Have you reported this to Fizzer? https://warzone.com/ReportBug
If you do that and send your logs, Fizzer will have more information than you can share on this forum. Fizzer could give you more detailed feedback based on what shows up in those logs for you. You might also want to specify in your bug report device details like what Android/iOS version you're playing on, etc. (That should all be in some "About" section in your Settings).
So now I have to buy a smartphone of the last generation just to play this game?
I don't think you need latest-generation. I have the WZ app on an Android tablet that is so old it doesn't even get security updates anymore, and I have not experienced any of the issues you describe. The cause might be more detailed than is obvious with the limited information here.
You could also check on your own device to see memory and other resource usage to determine why these crashes are happening.
Edited 2/22/2021 00:59:08