Changing number to new phone but keeping chat history When i tried backing up my old chat from google drive to my ne number on a new phone, it didnr detacted it. Does this mean i can only trasnfer chat if its the same number? If so how can i save my old chats on a new phone with a different number?
Chat history backup and restore feature can be used only to change the mobile device. Because the backup will be taken for the particular mobile number and can be restored in the same number.

how do i change my whatsapp number without losing chat history

There is an inbuilt option in the whatsapp messanger to change the phone number without losing the chat history. Please read the official documentaion to do the same.

https://faq.whatsapp.com/en/android/27585377
https://faq.whatsapp.com/en/android/28030001/?category=5245246