Need help fixing a critical error

We have a site that uses WordPress on GoDaddy Managed WordPress (Apache), sitting behind both Cloudflare and GoDaddy's own gateway cache. Theme is "Exponent Child."

My issue: The WordPress Customizer (Appearance > Customize) throws a fatal/backend error and won't load.

The site uses a plugin called Kirki, which gives the theme its design/customization controls. Kirki's maintainer (Themeum) rebuilt the plugin architecturally starting at v6.0.0 — it's effectively a different product under the same name. That rebuild broke backward compatibility with the Kirki_Control_Base class that the Exponent Child theme depends on. Because Kirki auto-updates, the site silently pulled the breaking version and the Customizer stopped working.

Possible fix presented to me: Roll Kirki back to the last compatible version (5.2.2) via the Plugins page, after taking a fresh UpdraftPlus backup, then disable auto-updates on that plugin to prevent recurrence.

Proposed long-term fix: Remove the Kirki dependency from the theme entirely

Another note is I am apart of the marketing team for this site and I have WordPress admin access but not hosting-level access. no cPanel, FTP, or PHP error log visibility.

This is also my first year of building and managing wordpress sites, so forgive me if this seems like that. Right now I'm trying to weigh my options to do a bandaid fix (roll it back), to try to remove the plugin dependency myself, or to ultimately outsource to another developer with more experience.

Thank you for taking the time to read my post.