Migration to Grav 2.0

When I press the "Stage & start wizard" button I get this:
Parse error: syntax error, unexpected 'o777' (T_STRING) in /var/www/html/migrate.php on line 574

My instance is a Grav v1.7.53.3 - Admin v1.10.59 running in a docker container.

How do I remediate?

I think you are running PHP 7.4. You need to be in 8.3 which is the minimum for Grav 2.0