Yes, Apple is still developing macOS Big Sur. They just released Beta 3 for version 11.5. At this rate, I think 11.5 might be released by the end of the month. I would like it sooner, but will just have to wait patiently. I have messed around in the macOS Monterey Beta, it is very buggy at this point. Hopefully, by Big Sur 11.6 most of the bugs will be worked out.