Hi there guys, So I have been dealing with this issue as well for the last couple of hours and tried all the things I found in this thread and on other places online. But unfortunately without any succes. So I had actually given up on it. I'm using the Razer Basilisk X Hyperspeed on a 2020 iMac with Big Sur 11.4. I just switched from a Catalina iMac where the mouse was working as can be expected. I have Bootcamp installed with Windows 10 for some light gaming. So I installed Synapse 3 on Windows on my iMac and got everything configured. I also read somewhere to lower the refresh rate for 2.4 GHz to 125 to help with the lag you experience when using it on MacOS. I did a fresh install of both the 2.4 and BT version of the mouse and on Windows it was working fine. Since that is where I use the iMac for gaming, I was maybe not as dissapointed as I would otherwise been. When I then switched back to MacOS I noticed that indeed the 2.4 mouse was working normally, nog lagging. So I also tried if I could couple the BT part of the mouse. And what do you know... it works! Just as well as on Windows. So this might be a solution for people running Bootcamp (or willing to install Bootcamp for this issue). No need for the Razer software by the way! Hope this might help for other frustrated folks!