You are using a very old version of Resolve. It's not compatible with Big Sur.
Please download and install the current Resolve 16.2.8 release version from here:
https://www.blackmagicdesign.com/suppor ... and-fusionIn the Latest Downloads column on the left, scroll down to Nov 25 2020 for the 16.2.8 versions. Make sure you download the Studio version, if you have a Studio activation key or dongle. If you have neither of those, download the free version, which is the one without Studio in the name.
If you are using new BRAW 12K files, you'll need to use the 16.3b3 version of Resolve.
Or, if you are feeling adventurous, you might want to try the Resolve 17.0b7 code. It's pretty stable at this point, and if you are just getting started, might be something to try.