I will spare you the full list of ridiculous bugs and kafka-esque dread that one encounters in using almost any newer flip phone-- which is baffling considering they were faster and smoother with many of the same features in 2009 than they are now.
When I try to open the KaiOS store to look for more apps, it loads to 99% and simply never loads fully. I've already tried rebooting without sim and then with, as well as registering and signing into a KaiOS account with my email.
Looking for solutions that don't involve just getting a smartphone. Yes I'm aware that "this is what you get" for opting out of the hamster wheel of planned obscolescence. There's literally no good reason why a powerful basic phone w/out bugs doesn't exist in 2021.
I encountered the same problem. The solution I found is to use the web browser to access the KaiOS website, which has an app store section. If you click on one of these apps on the website, it will pull up a page with a button to take you to the KaiOS Store app. This should get you into the store itself, which you can then navigate normally.
I share your grievances with this phone. I'm experiencing a couple serious bugs myself.