Yes. KiCad stable and KiCad-nightly can both be installed at the same time. This was a common request and has been fixed some time ago (months, maybe years).
When working with nightlies, I suggest to make at least a daily backup, and also before each “big” operation.
It can also help to backup the installation files of some different nightly versions. In that case, if you later install a “bad” nightly, you can un install it and revert to a backed up nightly. Serious bugs do happen in the nightlies, for example:
But they don’t happen often, and are also fixed quickly (often within a day).