And to get on topic, best place to download apps if you're not using Google Play Store would be from the officials app's website. Places like WhatsApp has its own apk file you can download as well as Telegram, and Signal. For other apps F-Droid is pretty good although people here will say F-Droid is bad.
You could also just make a separate profile with Google Play on it and download it from the official Play Store for apps that need Google.
Using other third party stores always come with a risk of putting malware on your phone so be aware of that and stay safe.