Korra I've contacted my web host, which is the best way to deal with this kind of problem. You need to change the version of php-cli. Depending on the host, this can be done using the cron command. For one of mine, all I had to do was change php php flarum to /opt/php82/bin/php flarum.
⚠️ It depends on your host! For others, you'll need to use SSH and indicate the php version to use in the .profile file.