Read on Twitter
Lots of people seems really curious to try out macOS Big Sure, so here's a quick and easy tutorial to give it a try with 0-risk (kind of) 
1. You need to get into the beta by installing a developer beta profile. You either do this with some friend or go to https://betaprofiles.com/ and install one (risky, brave, such wow, not recommended – it's your call).
2. Once the profile is installed, go to System Preferences > Software Update. You will see there's a new update, Big Sur. Download it. (the image doesn't show it because I don't have the profile installed).
3. Open Disk Utility, right click on your Macintosh HD disk and select Add APFS Volume.
4. Name the volume as you wish, do not touch anything else.
5. Once the Big Sur installer is downloaded and opens up, click next and accept all the things because you are desperate to try it out. Stop at this screen and select your recently created APFS volume.
6. Now you are done! Just proceed with the installation as any other macOS, which is basically looking to an inaccurate progress bar for 40 minutes.
7. To select which OS to boot from you can either do it by pressing Option key at boot time or define the Startup Disk here instead.
