Old installation, New Server, Lots of PHP errors

I’m running WordPress on my own servers. An old server went down and I moved my site to a new machine. In case it’s relevant, the main difference is that the old server was running PHP 5.6, while the new one is on PHP 7.3.

The site is displaying current articles, but mostly can’t be edited. As one example, on the sample page linked to, you can’t add a comment.

I have deactivated all plugins, changed my theme to Twenty Nineteen. I reinstalled WordPress (everything but the wp_content folder). Health Check Status doesn’t reveal any major problems. Troubleshooting mode has 0 Notices. I turned on debugging in wp-config.php. When I try to add a new post, the page doesn’t display correctly and I see the following errors on-screen, both with my regular theme and with Twenty Nineteen activated:

Notice: Trying to get property ‘post_type’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/post.php on line 6754
Notice: Trying to get property ‘post_type’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/post.php on line 6755
Notice: Trying to get property ‘ID’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/post.php on line 6759
Notice: Trying to get property ‘post_type’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/post.php on line 7000
Notice: Trying to get property ‘post_type’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/theme.php on line 3078
Notice: Trying to get property ‘post_type’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/theme.php on line 3307
Notice: Trying to get property ‘post_type’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/post.php on line 4653
Notice: Trying to get property ‘ID’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/post.php on line 4653
Notice: Trying to get property ‘post_type’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/post.php on line 4109
Notice: Trying to get property ‘post_type’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/post.php on line 675
Warning: Creating default object from empty value in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/post.php on line 713
Notice: Undefined property: stdClass::$ID in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/post-new.php on line 67
Notice: Undefined property: stdClass::$post_date in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/edit-form-advanced.php on line 173
Notice: Undefined property: stdClass::$post_date in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/edit-form-advanced.php on line 175
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/edit-form-advanced.php on line 231
Notice: Undefined property: stdClass::$post_type in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 1398
Notice: Undefined property: stdClass::$post_type in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/taxonomy.php on line 226
Notice: Undefined property: stdClass::$post_type in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/taxonomy.php on line 229
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/edit-form-advanced.php on line 543

In the sidebar that usually has the Draft and Publish buttons, these messages appear:

Notice: Undefined property: stdClass::$post_type in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 25
Notice: Trying to get property ‘cap’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 27
Notice: Trying to get property ‘publish_posts’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 27
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 41
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 41
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 41
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 43
Notice: Trying to get property ‘publicly_queryable’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/post.php on line 1976
Notice: Trying to get property ‘_builtin’ of non-object in /bns/wmdh/wmdh/brandwares/bestpractices/wp-includes/post.php on line 1976
Status:
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 94
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 115
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 115
Visibility:
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 152
Public
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 263
Notice: Undefined property: stdClass::$post_status in /bns/wmdh/wmdh/brandwares/bestpractices/wp-admin/includes/meta-boxes.php on line 329

The page I need help with: [log in to see the link]