Recovering from WordPress 5.5 crash
Backups are so important even if you are paying for a monthly plan with a service like VaultPress or Jetpack Backups, make a full local backup of your website before running updates on your website.
VaultPress and Jetpack can break your website with this update, Khürt Williams experienced that. I recommend UpdraftPlus for backups with at least the free version of the plugin and if you are on DO, do a full server backup. Do these backups before and after the updates.
If WordPress 5.5 gives you the white screen of death, you will need that backup. Using WP-CLI force a previous version install of WordPress and then repair the database. That should fix it and then you will need to wait for version 5.5.1-5.5.2 to update.