Hello @generosus ,
Thank you for the report. I was able to recreate the reported issue and informed our plugin developers for this. We can not provide an ETA for a fix. You should monitor the changelog of the future releases of the plugin.
With this said, please note that these are only notices and not actual errors. As such, they do not ion any way cause issues with any functions in a WordPress site.
For the second part of your question: The Managed version of PHP will be switched to a higher value once we establish that most sites hosted by SiteGround are made compatible to properly support PHP 8. Currently, there are still many sites that are not working well enough with PHP 8 and it is up to their developers to make their code fully compatible with the latest versions of PHP.
Regards,
Plamen.M
Tech Support Supervisor
SiteGround.com