The game starts minimized and can not be maximized

In the '..\SteamApps\common\Baldurs Gate 3\bin' folder, right click the game executable(s) (bg3.exe for Vulkan, or bg3_dx11.exe), select Properties, switch to the Compatibility tab and disable fullscreen optimization. That has been reported to fix this issue.

You may also want to check off the 'Override high DPI scaling behavior' option (set it to Application), run as administrator and maybe set a Win 7 or 8 compatibility mode. In Windows 7, check off the option to 'Disable display scaling on high DPI settings', disable desktop composition and run as administrator.

Are you shutting down all non-essential programs before launching the game? Things like anti-virus, firewalls, overlays from graphics tweaking or monitoring programs, as well as chat programs, have all been known to cause issues.

When the game is minimized, can you right click on the Task Bar button and select Maximize or Restore?

Try starting the Task Manager (Ctrl-Shift-Esc or right click an open area of the Task Bar), and in the Apps list try right clicking and select the Switch To / Bring To Front / Minimize / Maximize options. Hopefully, if the Task Manager forces it maximized, it will stay that way after you quit the game and restart.

Try lowering your desktop resolution, and limit the refresh rate to 60 (if it is higher), to see if that helps.

If applicable, disable Steam cloud support either globally or for only this game. For disabling Steam Cloud globally, within the client click on the Steam menu and select Settings, and then Cloud. Or just for this game: go to your Steam library and right click BG3 and select Properties, then switch to the General tab and check the Steam Cloud section. Alternatively, exit out of the Steam client, or Galaxy for the GOG version, and just start the game directly from the executable when required.

Try browsing to the 'C:\Users\<UserName>\AppData\Local\Larian Studios' folder and delete the 'Baldur's Gate 3' subfolder. The easiest way to get there would be to copy the following line into the location bar in Explorer and hit Enter: %LocalAppData%\Larian Studios This folder contains the saved games, profiles and configuration files. If you have saves, it is better to rename the folder. However, if you don't have any saved games that isn't an issue. Next, extract the replacement folder from this download into your '..\Local\Larian Studios' folder, and see if that will let you start the game properly.

The graphicSettings.lsx file is set to 1280x720 Windowed mode, Very Low quality preset and low audio quality, which you can change in the options manually, or hit autodetect. See if this gets the game working.

Try doing a clean boot and then test the game. Click Start, or hit WinKey-R, type in msconfig and hit enter; in the General tab, click Selective Startup, uncheck Load startup items (if required) and leave Load system services and Use original boot configuration options checked. Next, click on the Services tab, check the box to Hide all Microsoft services, then click the Disable All button (maybe make a note of which are currently enabled/disabled), then click OK and reboot the computer. Run msconfig again to switch back to the normal boot configuration.

If you are still having trouble, please reach out to Support with your dxdiags. Press WinKey-R, type in dxdiag and hit enter, then when it finishes loading click on the 'Save All Information...' button and save the report somewhere handy to then attach to your email to support.