First, while it shouldn't affect the speed, note that your Zotero data directory is still stored within the Zotero profile directory. That's no longer recommended, particularly on macOS, where it causes various problems, and it should have been automatically moved out of there automatically when you upgraded to Zotero 5. For some reason that seems not to have happened for you. You might see a button to migrate your data directory if you check the Advanced → Files and Folders pane of the Zotero preferences, but if not, or if it doesn't work, you should close Zotero and manually move the directory — the lowercase 'zotero' directory within 'Profiles/[8 characters].default' that opens when you show the data directory — to be named "Zotero" (with a capital 'Z') in your home directory, where Zotero should detect it automatically.

Assuming that doesn't help with the speed (which it shouldn't), how many total items do you have, including child items? How big is the zotero.sqlite file in your Zotero data directory? Is this on a Mac with a hard disk drive or an SSD? How much RAM does this computer have?

It's still very slow. I have a SATA Disk hard drive.

What year and model is this? Mac laptops haven't had spinning hard drives in many years. (I think the last one was the non-Retina 13" MacBook Pro from 2012, though they somewhat irresponsibly sold that through 2016.)

You didn't say how many items you have.

OK, right. Not much to suggest here. That's an old, slow computer with a spinning drive, and a sizable library. The performance is still a lot slower than what I would expect for a library of that size, but Zotero caches data at startup to keep its operation faster later. If you have the memory, your best bet is to keep it open to avoid all the data loading at startup.

Have you adjusted your full-text indexing settings from the defaults in the Search pane of the preferences?

You can try checking your database integrity from the Advanced → Files and Folders pane of the Zotero preferences, which will also try to optimize the database, and that may speed things up a bit and shrink down your dataabase. It may take a while to run, so do this overnight or when you won't need to use Zotero for a while.