Brave New Church has been busy trying to upgrade all Joomla installations to Joomla 4. It's not easy. If your church, school, or business is having trouble, don't abandon the website immediately. Call a reputable web designer who knows about Joomla updates and then wait for that person to suggest you abandon the website. Just kidding, kinda.
If you decide to upgrade to Joomla 4 from Joomla 3, here's my advice:
Update all extensions, templates, and whatnot. Clear the cache and look for more.
Update the database if necessary. This killed one of my upgrades to Joomla 4.
Run the checks for compatibility in the Joomla Update component. Delete any extensions on the list you don't use. You'll more than likely have to delete the ones you do use the hard way later. Some that I know don't work include the Powr extensions and Custom HTML Advanced. But I'd read that 90% of old extensions don't work.
Pray.
Run the update. Be happy if it's not the "White Screen of Death" epic fail. If the fail is just a problem with getting to all of your content and extensions with an ambiguous error message, then you just have to keep deleting extensions. But now it's in the database rather than on the admin page (because it's broken).
If you got the white screen, then go way back to restore the whole thing, because I'm not sure what works for that (besides restoring the whole thing).
Delete extensions one by one. Then create an article like I'm doing right now in order to make sure Joomla 4 can at least do that.
If none of this works for you, at some point you'll have to give up and jump on the Wordpress bandwagon.