@Luksus Apologies for the late reply.
I have carried out a reinstall (no wipe) using the ubports installer but it did not reinstall the missing Gallery app.

@Mario-CH Thanks for the suggestion.
This command updates all of the existing apps but it did not replace the Gallery core app that I chose to remove.

It's going from bad to worse:-
I tried to re-install just the Gallery app, so I used the App Store to remove the Gallery app but now it refuses to re-install.
I have installed an equivalent photo management app called Imaginario which works correctly.
There is definitely something wrong with the Gallery app.

@OtaDr I'm trying to avoid doing a full re-install. It isn't a big problem at the moment as I can get at my photos via the File Manager. I was hoping for a simple fix.

@MrT10001 Yes, I have rebooted many times. Still showing the black squares.

The gallery app on my Pixel 3a is showing black squares rather than preview thumbnails of my photos. The app was working correctly on 20.04 OTA2 but when I updated to OTA3 and now OTA4 the thumbnails were replaced by black squares.
Can anyone suggest what I have done wrong and how to fix it?
FYI:- File Manger app shows thumbnails correctly for all the image files in my Pictures folder.

@RayCulp PM sent to you.

@Keneda Thanks for the info but I think that will give this a miss. I don't want to push my luck, and am content with what I have achieved so far.

Yes! That seems to have (mostly) worked: I now have 'user-data' copied off my broken phone and onto my laptop. Thank you everyone for your help.

Now the bad news:- Pushing the data onto my replacement phone did not work very well.
I bought a replacement Pixel 3a of the same spec. Down grading to Android version 9 was a bit of a struggle as the Android Flash Tool kept failing repeatedly due to a 'Network Error' while downloading the new image. I eventually got it too work by swapping to a computer that had an ethernet connection to my router, rather than using wi-fi, and that worked first time. Installation of Touch (version 20.04) worked well, the only small problem being that the phone was not automatically recognised when I first started the installer. I was also able to push the 'user-data' from my laptop onto my newly set-up replacement phone, but this broke several of the installed applications! Gallery and Music would not open at all, and Messages was so corrupted that I could not read the texts. The only good result was that Contacts worked and I have been able to export a copy to my laptop.
I understand that there is quite a big difference between the operating systems on Xenial and Focal, so I can only assume that there is also a difference in the contents of the hidden config files in the 'user-data' folder between a phone that has been upgraded compared with a phone that is a fresh install. And that it is these differences that have caused certain apps to fail.
I have reinstalled Focal on the new phone, and wiped the user data. I now have a phone that works as expected. I shall copy photos, music, and contacts over using the standard MTP service. I will also have to accept that the old text messages are lost. I am content with this; a 95% recovery of data from a broken phone is a good result. Thank you all again.

@Keneda Oops! My mistake! I shall try again in a short while.

@arubislander Thanks for the help. I did finally manage to get into Recovery Mode but, when accessing the phone system, found that the /data was completely empty! Either the phone is more broken than I realised, or I have accidentally wiped the original install during my random button pressing as I initially tried to get into the phone.
Am, I missing something?
Please note that I updated the phone from Xenial to Focal rather than doing a re-install. Could that have moved the data somewhere strange?

My apologies for not getting back sooner but I had to leave the phone for several days to let the phone battery completely run down so that I could be sure it was turned fully off.

@MrT10001 Thanks for the reply.
I shall try this as my last resort; the online instructions suggest that it can be quite tricky.

@xet7 Thanks for the reply.
The cost of a replacement screen is much higher than a replacement phone (second hand) so I have not considered it.
I shall try and connect a keyboard and mouse but the blank screen means that I have no feedback on my actions. Can you suggest what gestures I need to perform to unlock the screen in this way?

@arubislander Thanks for the reply.
I cannot remember if I have enabled Developer mode. Running "adb devices" in a terminal on the laptop does not show my phone to be attached.
What should I do to boot into Recovery Mode? The broken screen means that I cannot shut down the phone, nor do I get any feedback on my actions.

Hi All,
I'm looking for advice. Today I dropped my Pixel 3a and broke the screen. The screen is completely black with no signs of life. I cannot see if the phone is On or Off, or what mode it is in.
I would like to be able to access the file system so that I can copy the photographs etc to my laptop. But, when I connect the broken phone using USB, I am unable to unlock the screen so am unable to access the file system.
Can anyone suggest how I can use the USB connection to force unlock the phone?

My phone has an up-to-date install of Focal. My laptop runs Linux Mint 20.
Thanks.

@barryt I have been running 20.04 Development channel for a few days now and everything is working perfectly; SMS messages come through in just a few seconds. I shall post on the Github link.
Thanks for the help.

@lduboeuf I have updated to 20.04 Development channel. The system immediately delivered two texts that had been sent the previous day, which is encouraging. I shall test it for a week and then report back here and on Github.

@lduboeuf Thanks for the reply.

16.04 (OTA-24), and stable channel.

I also have this issue on my Pixel 3a; it has recently stopped receiving text messages, making using 2FA a major problem. I can send texts and make calls without a problem. A restart is sometimes a temporary fix but the problem keeps coming back.
Has this bug been reported on GitHub?

@alter Thanks for the information. I have made a suggestion for a change to the hash symbol. We shall have to wait and see if anything happens.