As you already know, your iMac can not run the newest MacOS anymore (the last one it can run is Ventura). At one point in the future (if you want to update your current software) your software won't run on your iMac anymore because it needs a newer OS than your computer can run. For your music production software that can become a problem if you can't run updates on your computer anymore. If you don't mind to use 'old(er)' software for years to come it won't be a problem, but if you want (for instance) to upgrade your music production software in the future that can potentially be a problem.What do you mean by software and OS updates being the biggest bottleneck? are you saying that I should have the iMac updated, and should update it to one of the updates I was recommended?
But don't overthink it! If you are happy with software you are running now, simply keep running what you have now. Make backups and be happy for many years to come.