My wife got tired of the slow work of her MacBook Pro and looked at how my small (and also old) ThinkPad works, poked her finger and said “I want the same.”
As a result, her laptop is now running EndeavourOS KDE. Not everything worked out right away, and the system can only be started with an LTS core. But it works!
Faced the same problems as @doggie. Nevertheless - it works!
P.S. @doggie, thank you for the experience and the hint 
So did EndeavourOS KDE give her the speed she wanted? Hopefully so, as they say “Happy wife, Happy life”.
Pudge
KDE? 
Edit: I guess MacOS is gone?
Good question 
There was no goal to get the maximum speed of interaction with the system. There was a task to get more speed than El Capitan gave on this laptop. And it was achieved - the system loading speed, as well as the overall speed of interaction with the system, is higher with EndeavourOS on board. At least so much that it no longer irritates the wife 
Yes. I haven’t been able to get along with any other DE 
And again, yes 
Being in a live environment, I completely deleted the partitions from the HDD and gave it completely into the possession of EndeavourOS 
I did the same 'cause Apple computers don’t need MacOS anymore 