We'll add solutions to common problems to this topic as we come across them. If the answer to your problem is not here, please post about it in the support forum.

Questions answered below:
-Where is Config.txt located?
-How can I switch graphics settings without starting the game?
-How can I run in Exclusive Fullscreen mode?
-What is VSync?
-I keep getting the "Couldn't load cloud save" popup on startup. What can I do?

Where is Config.txt located?
The startup configuration file Config.txt is located next to the executable. To find it, right click the game in Steam, go to Properties, then to the Local Files tab and click Browse Local Files.

How can I switch graphics settings without starting the game?
You can edit the file Config.txt in Notepad to change things like the resolution and whether the game uses DirectX or OpenGL. You can also edit these settings in the in-game menu, so normally there is no reason to edit Config.txt in Notepad.

How can I run in Exclusive Fullscreen mode?
Exclusive Fullscreen is not given as an option in the menu because videocard drivers often have problems with this, especially in combination with alt+tab. However, if you really want Exclusive Fullscreen you can get it by setting isExclusiveFullScreen=1 in Config.txt. In general we recommend not doing this and instead using Borderless Window for fullscreen, since this is much more stable and instant when doing alt+tab.

What is VSync?
VSync makes the game run at the exact same framerate as the monitor. This makes the game look most fluent and prevents ugly screen-tearing effects (horizontal lines in the screen). Most modern monitors run at 60fps (frames per second), but some people prefer to run on a much higher framerate. To do so, disable VSync. When you have a fast computer and have disabled VSync, the game might run on 200fps or more. This does not look any more fluent, because your monitor cannot show this, but to some players the controls feel slightly more reactive and faster on the higher framerate. Also, if you have a slow computer then turning VSync off will give you higher framerate, since VSync caps the framerate to full monitor frames, so if you drop below 60fps, VSync will cap the framerate down to 30fps (or 20fps or 15fps below that).

I keep getting the "Couldn't load cloud save" popup on startup. What can I do?
Whenever we've seen this issue come up, it was caused by an outdated Steam. Please check your Steam version by going to Help -> About Steam in the Steam client - it should be at least from October 2018 at the time of writing. If it's not, please update your Steam installation manually. The easiest way to do this is to close and exit Steam, go to your Steam install folder (by default located in C:\Program Files (x86)\Steam) and delete everything except Steam.exe and the userdata and steamapps folders (which contain your save data and game installs respectively), then run Steam.exe. This will force a Steam client update, after which the game should work again.
If for whatever reason you can't delete all files, please restart your PC and try again. If this still doesn't work, a full Steam reinstall may be necessary.