Mac book air Admin account slower than fresh brand new user account — I have tried a lot to fix
&quot;Do you have any other ideas or is it reformat and rebuild time? I haven’t done a fresh install in 10 years and really want to avoid
this.&quot;

If the problem does not appear in a brand new user account, then there is absolutely no need to erase the disk and reinstall the OS. The OS works fine: only the user account is affected.
Some may suggest packing up and moving to a new user account. The trouble is that if you keep doing this every time you come up with a user-account problem, you'll have a succession of different user accounts, which may cause problems with backups, file ownership attributions, etc. And you'll be none the wiser.
The cause is something in the user's Library folder. It could be third-party software that's set to launch at startup, so test by disabling ALL of that. Don't leave any 'necessary' stuff.
You've deleted the entire user Preference folder, which is overkill. I would test whether things improve after you remove the folder, and then restore it if they don't. Move on to the next folder.