Correct, as Bluetooth is a backwards compatible protocol, you have to connect to oldest first.
If you connected to newer first you have to reboot the buds before connecting to older. As the buds default to connecting to last connected first means you have to turn Bluetooth off of last connected.
It’s far simpler to just own multiple audio products and dedicate to specific devices. Or be a geek.
When people say replacement buds worked, or say they worked for a while, often it’s this very reason.
The ultimate fix is multiconnect across multiple Bluetooth versions concurrently but that adds cost. Then the complaints are different.