Broken post editor after WP 6.2 upgrade (custom theme)

Greetings, after last night’s automatic upgrade, post/page edit interface stopped loading. Browser console has a couple of these errors:

TypeError: e.forEach is not a function
    T 
    useMemo 
    useMemo 
    xo 
    kt 
    js 
    kl 
    yl 
    vl 
    ol 
    ul 
    v 
    ce 
    jQuery 11
react-dom.min.js:10:53541

Additionally, I see several odd PHP errors being logged:

[30-Mar-2023 11:59:19 America/New_York] PHP Fatal error:  Uncaught Error: Undefined constant "ABSPATH" in /var/home/fmglaw.com/www/public/wp-includes/blocks/index.php:8
Stack trace:
#0 {main}
  thrown in /var/home/fmglaw.com/www/public/wp-includes/blocks/index.php on line 8

[30-Mar-2023 11:55:55 America/New_York] PHP Fatal error:  Uncaught Error: Call to undefined function get_the_block_template_html() in /var/home/fmglaw.com/www/public/wp-includes/template-canvas.php:12
Stack trace:
#0 {main}
  thrown in /var/home/fmglaw.com/www/public/wp-includes/template-canvas.php on line 12

[30-Mar-2023 11:51:09 America/New_York] PHP Fatal error:  Uncaught Error: Class "WP_Widget" not found in /var/home/fmglaw.com/www/public/wp-includes/widgets/class-wp-widget-block.php:17
Stack trace:
#0 {main}
  thrown in /var/home/fmglaw.com/www/public/wp-includes/widgets/class-wp-widget-block.php on line 17

None of the paths seem specifically related to the custom theme we use, but when I tried switching to TwentyTwentyThree theme, I was able to see the editor again.

Any assistance would be greatly appreciated. This is a live production site.