Ah I see strange, will take a look at it.
As a workaround you can try to create a file ‘arcbrutile_pro_settings.xml’ in the AppData directory (like C:\Users\your_profile_profile_name\AppData\Local\arcbrutile_pro\arcbrutile_pro_settings.xml) with following content:
<?xml version="1.0" encoding="utf-8"?>
<AppSettings xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" >
<MapBoxKey>your_map_box_key</MapBoxKey>
</AppSettings>
Replace ‘your_profile_profile_name’ and ‘your_map_box_key’ with the correct values.
