Hi @stavrosomo,
thank you very much for the screenshot of the error.
It looks like the Action Scheduler library that is used in our plugin (and also in other plugins, like WooCommerce, …) can’t create the database tables it needs on your server.
It’s strange because we are using the Action Scheduler library for a long time (since version 2.1.0) and as I can see you are currently using version 2.8.0. I don’t know why this error was not causing issues on your site sooner.
Are you using any other plugins that might be using Action Scheduler library? Like WooCommerce or some other plugin?
Here is a guide on how users with this similar issue could resolve it: https://wpmailsmtp.com/docs/how-to-troubleshoot-action-scheduler-issues-wp-mail-smtp-2-1-1/
But do know, that if your server is causing issues and not allowing to create these DB tables, then the installation & activation of the Action Scheduler plugin (the standalone plugin mentioned in step 2 of the guide), your site might also cause a fatal error and you’ll have to restore your site again.
Do you maybe have a staging site, you can try these things out?
Take care!