Why did Adobe Flash Player get discontinued, and what are the safest modern alternatives to run old Flash games and content today?

I am trying to understand why Adobe Flash Player was discontinued and what are the safest modern solutions to access old Flash-based games and content. Many older websites and games still rely on Flash, but modern browsers no longer support it. I want to know the reasons behind its removal and the best secure alternatives (like emulators or tools) that can run Flash content today without security risks or outdated plugins.