Thank you for taking the time to post and welcome to the Bose Community!
I'm sorry to hear of the issues you are experiencing with the Audio Video lag when you connect your QC35 II to your iMac. I can imagine how frustrating this must be for you and I'll do all I can to assist you!
I have located a previous thread from the Community that may be helpful to you. You can find the LINK HERE.
I would encourage you to give it a read and try the troubleshooting steps mentioned. Hopefully, there will be a solution in there for you. If not, please reach out to us again and we will see what else we can recommend.