For what it is worth to newbies or others:
I created a backup micro-SD (reading so much about SD death). I followed the instructions on this page, using the 32bit Rpi 3 image (I have an RPi B+). I am using an M1 Mac with Big Sur. My new micro-SD is a SanDisk 128GB MAX Endurance microSDXC Card (SDSQQVR-128G-GN6IA).
My old version of BalenaEtcher had some problem, so I downloaded the latest.
I ran into the problem of the Rpi not booting with the new SD. One or two bumps of the green LED, then just the red LED. No LAN led activity. The Rpi was not observed on my LAN (using Lanscan).
I re-flashed the SD with a bit more luck. I could see the Rpi on LanScan, but could not access 192.168.1.61:8123 (or any of the other variants). For both flashes, Balena indicated a successful flash.
On a third flash try, I had problems using BalenaEtcher - window was blank after choosing the target disk. So I downloaded ApplePi-Baker v2.
I re-download the HASS image and successfully flashed.
Plugged in the micro-SD, and after a while of LAN led and green led activity, I accessed 192.168.1.61:8123. It showed a message that HASS was setting up.
It then asked for me to create a new account or restore from a snapshot. I restored and everything was there.
I am not sure why BalenaEtcher did not work, nor why the flashed SD failed. Maybe there is something funky with Mac M1, or maybe it was just poor reliability with Rpi and SD cards.
I did stop HASS prior to pulling the power on the Rpi. I returned the old SD to the RPi, solid red led after green and LAN led activity, and all is well.