The launcher is blank or empty

Try verifying local files: in the Steam library, right click on the game and select Properties, switch to the Local Files tab and then click on the 'Verify Integrity of Game Files...' button. If you are using the GOG version, in the Galaxy client, select the game, then the settings icon at the top right, beside the Play button and under Manage Installation, select 'Verify / Repair'.

Try starting the launcher directly from the '..\SteamApps\common\Baldurs Gate 3\Launcher\LariLauncher.exe' executable. For the game, try optionally exiting out of the Steam client and starting it directly from the '..\SteamApps\common\Baldurs Gate 3\bin' folder, by right clicking the executable (bg3.exe for Vulkan, or bg3_dx11.exe) and running as administrator.

Try resetting the launcher in the options (button with the gear icon in the bottom left of the launcher window), then exit and restart the launcher. If that helps, there should be a 'get started' button to click on, and then you can either create or log in to an account, or there should be a button to skip creating an account in the lower right, along with a checkbox to not ask again.

Try copying and pasting %LocalAppData%\Larian Studios into the location bar in Windows Explorer, hit Enter, and then in that folder delete or rename the 'Launcher' folder and try starting the launcher again. If that helps, the first time the launcher starts it may take a little longer, as the cache is rebuilt.

Temporarily disconnect from the internet and see if that gets the launcher working. If it doesn't get a response checking for updates, there should be an offline version of the launcher page shown.

If that does not help, please copy and paste %LocalAppData%\Larian Studios\Launcher\Logs into the location bar in Windows Explorer, hit Enter, and from that folder contact Support with the runlog.txt file.