That fixed it. Thank you.
Needed to do what you mention in your link:
Uncomment “error_log = php_errors.log” in my php.ini file, which in my case was found in /etc/php/7.4/apache2
Reproduced the blank page error and saw this is in php_errors.log:
[27-Feb-2021 21:43:59 UTC] PHP Parse error: syntax error, unexpected '=>' (T_DOUBLE_ARROW), expecting ')' in /var/www/html/custom/modulebuilder/packages/custompackage/modules/submission/metadata/subpanels/default.php on line 20
Removed the offending line and we’re back in business.