I have the iPhone XS Max, it appears I can connect to 2 Bluetooth speakers at same

You're welcome. There is an exception to this, where you buy speakers which are slave and master, meaning they are tied to each other, so when you stream music to one, both will play. Otherwise, it's one speaker at a time.

The two speakers must allow them to be paired (act as one Bluetooth device).

You can be paired to lots of Bluetooth headphones and speakers, but you can only use one at a time.

You're welcome again. Apple Home Pod speakers are an example of this.