After installing a security update, my device won’t boot. Is there a way out of this without losing my data?

In more details:

My device is a Moto e7 XT2095-2 with Android 10.

Today I got a notification for the latest security update. I downloaded it. My phone tried to restart but failed, and looped several times.
In the end it displayed a black screen with a barcode and “fastboot mode ...”.

After trying to reboot again, now I’m getting this message:

Android Recovery
motorola/malta_reteu/malta
10/QOFS30.569-36-31/095c7
user/release-keys
Use volume up/down and power
Can’t load Android system. Your data may be corrupt. If you continue to get this message, you may need to perform a factory data reset and erase all user data stored on this device.

If I select “Try again”, I’m getting an “Error!” screen then the device reboots (tries to, I mean).

The device is not rooted. I haven’t unlocked the bootloader, installed a custom ROM, or a custom recovery.
Developer options are enabled – that’s the only difference from the average person’s smartphone.

I have no backup of my data.

I know very little about Android, but as a developer I’m comfortable enough learning about it.

I searched online what I could do, and tried to ADB sideload the stock OTA as described here:
https://www.droidwin.com/fix-cant-load-android-system-your-data-may-be-corrupt-without-reset/

with the 2 latest files from here https://mirrors.lolinet.com/firmware/moto/malta/official/RETEU/

On my laptop terminal, I got this:

serving: 'update.zip' (~0%) adb: failed to read command: Undefined error: 0

And on the device:

Finding update package…
Opening update package…
Verifying update package…
E:footer is wrong
Update package verification took 0.2s (result 1)
E:Signature verification failed
E:error: 21
Install from ADB completed with status 2.
Installation aborted.

I’m a bit confused from reading a lot of contradictory information. Is this method supposed to work or is it failing because my bootloader is locked or because I’m using the stock recovery?

Is there a way to fix this bootloop without losing my data? Is there any way to backup the device’s data before a factory reset?

I would really appreciate if someone could point me to things worth trying!

Thanks