Joe King Thank you for the suggestions, I use only one Whatsapp account, I don’t use any other 3rd party file manager apps, I tried re-installing WhatsApp, then it worked fine for 2 minutes (I tried sending a video, that video was sent, when I tried sending a second video, again the issue started).
Just now my phone got randomly switched off and the screen said “Nothing crashdump mode (minidump)"
I don’t understand what’s wrong with my phone. My phone is just 30 days old.