Answer four questions about what you see and get the most likely cause, with checks you can run yourself today. No signup, no crawl of your store.
Not how long until it is finished. How long the screen stays blank.
Plenty of tools will crawl your site and hand you a score. We deliberately do not, for two reasons. A single automated test measures one page on one simulated device, which is the least useful kind of performance data. And the number it produces tells you nothing about which of several possible causes is yours.
Four questions about what you actually observe get closer to a useful answer than a score out of a hundred, and you can act on the result today without waiting for anyone.