Disable WLAN0 (internal); Enable WLAN1 (ext) at boot

Support & Help Requests Raspberry Pi
1

I've added a USB external antenna (BrosTrend Model: AC3 V2) which works (it reaches easily across the living room: some 24 ft, which the internal barely manages).

The internal antenna shows up as "Wi-Fi Network (BCM43438 combo and Bluetooth Low Energy)" under the networking icon in the upper-righthand corner of the desktop. This particular external antenna shows up as "Wi-Fi Network (Realtek Wi-Fi)".

There is no information about which is on wlan0 and which on wlan1, but I have determined that wlan0 is the internal antenna's port.

I've found that, although the conventional 'ifdown' command is present in the RPi4 version of Ubuntu Mate, it returns "ifdown: unknown interface wlan0". However, this
alternative works:
% ifconfig wlan0 down

I would like to ensure that wlan0 and eth0 are down after booting and wlan1 is up.

Q. How can wlan0 and eth0 network ports be disabled, and wlan1 enabled, at boot time?

Actually, this may be a BAD idea, if disabling wlan0 also disables Bluetooth, which appears it might. (I suspect Bluetooth is needed for tethering to a smartphone for internet access, but I've still to research that.)

Alternatively,
Q. How can wireless connection be made, PREFERENTIALLY, to wlan1 at boot, leaving wlan0 up (and available for Bluetooth, if in fact it serves BT)?+

2

Put more simply:

Under the Networking icon, under Edit Connections, (regardless of whether it is wlan0 or wlan1), I am only offered a choice to
"Connect automatically with priority [number]"
as an option for SSIDs, e.g., "Joe's Wireless", but NOT for wireless PORTS, e.g., wlan0, wlan1.

I stumbled upon netplan and edited a copy of:
/etc/netplan/01-*
to add lines defining "ethernets:" and "wifis:" and some connection specifics which
subsequently show up under the Networking icon (U-R corner of Desktop), accessible via
Connect to Hidden Wi-Fi Network...

It works, for I'm composing this using one of those netplan definitions.
[EDIT: "It works," but only in the sense that they show up under the Network icon; "connecting" them connects them to something called "opennetwork"--which I naively assumed would be "strongest signal available on an uncrypted channel." Not so.]