I tested this issue myself and I was able to reproduce it from the Network Dashboard > Snippets, when editing an activated snippet and try to update it after enabling the “Allow this snippet to be activated on individual sites on the network”.
Here is the error trace:
[21-Sep-2023 22:31:23 UTC] PHP Fatal error: Uncaught Error: Object of class Code_Snippets\Snippet could not be converted to string in public_html\wp-content\plugins\code-snippets\php\snippet-ops.php:245
Stack trace:
#0 public_html\wp-content\plugins\code-snippets\php\snippet-ops.php(245): array_diff(Array, Array)
#1 public_html\wp-content\plugins\code-snippets\php\snippet-ops.php(554): Code_Snippets\update_shared_network_snippets(Array)
#2 public_html\wp-content\plugins\code-snippets\php\rest-api\class-snippets-rest-controller.php(270): Code_Snippets\save_snippet(Object(Code_Snippets\Snippet))
#3 public_html\wp-includes\rest-api\class-wp-rest-server.php(1188): Code_Snippets\REST_API\Snippets_REST_Controller->update_item(Object(WP_REST_Request))
#4 public_html\wp-includes\rest-api\class-wp-rest-server.php(1035): WP_REST_Server->respond_to_request(Object(WP_REST_Request), '/code-snippets/...', Array, NULL)
#5 public_html\wp-includes\rest-api\class-wp-rest-server.php(447): WP_REST_Server->dispatch(Object(WP_REST_Request))
#6 public_html\wp-includes\rest-api.php(418): WP_REST_Server->serve_request('/code-snippets/...')
#7 public_html\wp-includes\class-wp-hook.php(310): rest_api_loaded(Object(WP))
#8 public_html\wp-includes\class-wp-hook.php(334): WP_Hook->apply_filters('', Array)
#9 public_html\wp-includes\plugin.php(565): WP_Hook->do_action(Array)
#10 public_html\wp-includes\class-wp.php(398): do_action_ref_array('parse_request', Array)
#11 public_html\wp-includes\class-wp.php(779): WP->parse_request('')
#12 public_html\wp-includes\functions.php(1335): WP->main('')
#13 public_html\wp-blog-header.php(16): wp()
#14 public_html\index.php(17): require('public_html\...')
#15 {main}
thrown in public_html\wp-content\plugins\code-snippets\php\snippet-ops.php on line 245