But why does no bitcoin app exist like this anymore?
Surely someone has made one?
Why is it so hard to program the bitcoin app to send the funds back to the original address instead of a different change address? Or was it made impossible somehow over the years??
Call it:
Single Wallet: Bitcoin Classic

Please I find it so hard to believe this great control and feature of bitcoin has just been wiped out!!
I can't breath!

Again, I don't suggest it, but you can:
1. Create a paper wallet offline. Disclaimer: you MUST know what you are doing.
2. Back up the private key, obviously in physical form.
3. Get the address and import it to BlueWallet. You will always be able to send funds to this address.