I am very well versed in programming and understand fully that applications may not work if they were designed for older versions of macOS, but you are talking about something different to what this thread and my questions are about. I am talking specifically about slow down.
You were clear above that migrating only the user account and intentionally excluding applications would result in a faster system with less slowdown.
You said that in response to my question about why the new user account ran faster with Final Cut than my current user account.
I am arguing the perspective that it is only additional apps that I like to have running in the background that cause a bit of slow down. You are saying that I could achieve the same speed increase by migrating and excluding the applications then spending painful days setting up all my preferences, keyboard shortcuts, toolbars, Etc back to how I want them. I am arguing respectfully that that is a waste of time.
I linked to you to another thread where a level six contributor stated that he agreed with that being a waste of time and stated that it sounded more like advice you would get for a Windows system.
I have asked people this question in the past and I've never got a clear answer. you are still not giving a clear answer, with all due respect. I asked you why excluding applications from migration would cause the system to run faster. you answered this by explaining why it might prevent crashes. Talking about crashes is not an answer to a question about slow down.
If I open Final Cut Pro, what is Final Cut Pro looking at from my older applications that is causing it to slow down? I don't think it interfaces with the old apps at all.
When I provided the Etrecheck you mentioned 2 kernel extensions. I removed these and the system did not speed up.
I remain open to the possibility but until someone can give a clear answer as to why excluding applications during migration will cause the migrated system to run faster, even one month later when all of those applications have been reinstalled and eight of them are running in the background, then I cannot understand it. can you give a clear answer as to why excluding applications from migration would result in Final Cut Pro running faster one month later?