upgrade from Catalina to Big Sur 11.5 (not 11.6) needed/ sound eruptions

Avid Media Composer 2021. 9 is only compatible with Big Sur 11.5.x, not 11.6. I need to upgrade from Catalina, but only to 11.5. Is that possible?

Talked to Apple, but didn't get a solution for that.

The reason? The Avid MC 2021 9 has caused a wildly brutal sound eruption through speakers on 4 occasions - sound preferences are set to headphones, not speakers. Tried a restart and the noise happened threefold when starting up. What can be the cause? This started three days ago after upgrading from MC2021 6 to 9.

Specs:

  Model Identifier: iMac20,1

  Processor Name: 8-Core Intel Core i7

  Processor Speed: 3,8 GHz

  Number of Processors: 1

  Total Number of Cores: 8

  L2 Cache (per Core): 256 KB

  L3 Cache: 16 MB

  Hyper-Threading Technology: Enabled

  Memory: 72 GB

Randi

Norway