WP 5.5 doesn't work with our version of Stackable blocks

[cjyabraham]

Our current version of Stackable v1.17.3 is old and breaks the editor after upgrading to WP 5.5. We had been putting off getting rid of Stackable but knew that an issue like this would eventually arise. In order to upgrade to the latest WordPress, we'll need to do one of the following:

1. Get rid of Stackable. As examined previously, this is a complex operation but the sooner we do it the easier it will be. Additional blocks will need to be written to replace the lost Stackable blocks and meet the existing needs of the Events team. A partial move off Stackable will no longer be possible as this old version of the plugin now makes the WordPress 5.5+ editor unusable. All existing pages will need to be migrated by hand to no longer use Stackable blocks.
2. Upgrade Stackable to the latest version. When we last tried to do this it broke a lot of our event sites so that's why we've been staying on the current version. We think that Stackable is evolving into a huge and complex set of blocks that would increasingly weigh the site down so we'd prefer to get off it entirely.
3. Try and fix v1.17.3 of Stackable so that it works with WP 5.5. We don't have the source code for Stackable so we'd need to get it. This could be a lot of work and it may not even be possible. We may then need to keep doing this as we upgrade to later versions of WP.

[cjyabraham]

Current usage of Stackable blocks:

[cjyabraham]

Plan for executing option 1, getting rid of Stackable:

• Develop a migration plan for each of the ugb blocks used on the site; if necessary, update styles and develop new blocks to provide a suitable substitute
• scan the code for any ugb styles hardcoded into code, such as here; once we drop the Stackable style sheets these items will no longer be styled
• Setup demo of kubecon homepage using new blocks
• Train Megan on using the substitutes to ugb blocks
• Have Data Person migrate all ugb blocks to appropriate substitute (note: Group blocks won't have gradients until the WP upgrade); start with the oldest first so that the live events will have non-gradient Group blocks for the shortest time possible.
• Deactivate and uninstall Stackable
• Upgrade WP to v5.5
• Set gradients of all Group blocks to match what we had on the Stackable Container blocks

WP 5.4 block analysis
WP 5.5 block demo

[cjyabraham]

Closing in favor of #578