Thanks for stopping by the Apple Support Communities. From your post, I understand that you are having trouble signing into the Guest user on your MacBook Pro. In addition, you seem to be unable to cancel and switch to your own user account. I'm happy to help!
Based on what you've described and shown with your screenshot, I would recommend the following steps. Try each in order, testing after each step:
- Restart your Mac. If you are able to, click Cancel on the screen your post shows, then select Restart. If you are unable to do that, you can restart your Mac by pressing and holding the Power button for about 10 seconds, until it shuts down. Once it is off, press your Power button again to turn it on. Then, try logging in.
- Reset your computer's NVRAM and SMC. More information on these processes, including what they do and how to reset them, can be found here: How to reset NVRAM on your Mac - Apple Support and How to reset the System Management Controller (SMC) on your Mac - Apple Support.
- Try logging in using safe mode: Use safe mode to isolate issues with your Mac - Apple Support.
If you are still having trouble after the above steps, do not hesitate to respond back. If you do, please include some information about what happened when you tried the above steps.