Hello Daniel,
Thank you for reaching out. Based on your description, it seems the text color issue in the selection windows may be related to the current administrator theme settings. I recommend switching your administrator theme from light to dark mode prnt.sc/Prf-CjsVbEfD, as this might resolve the "white on white" text display issue.
As for the absence of Great Britain in the country selection, it might be labeled under a different name or setting, such as "United Kingdom." Please check the list again or let us know if the issue persists.
If you encounter any further challenges, feel free to reach out. We're here to help!
Best regards