Google Maps on my Pixel Tablet is unable to get a fix on my location. The crosshairs icon at the bottom-right that can be tapped to centre the map on your location is black and has no dot in the middle and there is no blue dot on the map showing my location. Tapping the crosshairs has no effect.

I'm using the owner profile with Sandboxed Google Play installed. Location requests are not rerouted to the OS and Google Play Services has all the permissions necessary to provide high accuracy location. Improve location accuracy is enabled. All the location settings are the same as on my Pixel 6, on which Google Maps has no problem getting my location.

Another mapping app, OS Maps, is able to instantly get an accurate location fix on the tablet, even when indoors with poor visibility of the sky.

Can anyone suggest what might be the problem with Google Maps?

The Pixel Tablet has no GNSS receiver, so unlike on your Pixel 6, the only way to get location is via Google Play Services.

The instructions for configuring that are given in the link below, but it sounds like you have things set up correctly, especially if you are getting location on the Tablet via another app.

https://grapheneos.org/usage#sandboxed-google-play-configuration

One additional thing you could try is enabling Bluetooth and WiFi scanning under Settings > Location > Location services. I believe those settings can be used by Google Play Services, when enabled.

    treequell The Pixel Tablet has no GNSS receiver

    I hadn't realised that! It'll be useless for navigating when out in the countryside and away from WiFi signals then.

      TheJase It'll be useless for navigating when out in the countryside and away from WiFi signals then.

      Correct.