Scheduler not working

The Grav scheduler doesn't work, giving me the error above:

I talked with my host but they said they couldn't enable proc_open for security reasons.

Is there any way to make it work without allowing proc_open?

You can use an alternative backup method:
Sync your site with e.g. lftp to your local machine and from there it goes to your daily backup on an external HDD or NAS. Any sync software will do, because there are no database dependencies. You can use your local cron to trigger the backup.

Yeah, that works for backup, but what about other Grav cron (clear cache, for example) and email caching before sending it (the actual reason I went to that page)?