I want to transfer my whatsapp data and chats from my old android device to my new apple device

Based on information from WhatsApp, it is not yet possible, see: 

https://faq.whatsapp.com/general/account-and-profile/about-changing-phones

There are third party apps which support android to iOS WhatsApp transfer

Frankly, I don't know, never use third party app(s) on my iPhone.

I use a third party app -> iMazing (is not free) on the computer, then make a back up through iMazing.

iMazing will save all WhatsApp chats on the computer, but will not transfer to the iPhone.

I paid some money and tried out Mobitrix WhatsApp Transfer

[OFFICIAL] Mobitrix WhatsApp Transfer- Backup & Restore WhatsApp to Any Phone

It hasn't worked out and now I might have lost my backup on the original phone. Sigh.

But a bunch of other people reccomend this, so it must work for some people?