Seamless transfer of data and WhatsApp between iOS and Xiaomi

Hello Team,
Honestly, I have little experience with Android devices. I transferred all data for aunt from ios to samsung android a year ago. Everything was easy thanks to the Samsung Smart Switch Mobile app. App on both phones, cable in (cable USB-C to Lightning) and transfer. Done quickly and easily.

Now I bought a Xiaomi note 11 for my grandma. Actually only because it is cheap and the battery is new. Unfortunately I forgot to send it back.(14 days)Returns are no longer possible.

Is there an app for the Xiaomi like Samsung to be able to transfer everything. Especially whatsapp content.

What app can I install on iOS to transfer Whatsapp data?

Thanks.