CANNOT ACCESS OFFSET OF TYPE STRING ON STRING

I just wanted to let you know that I am in process of investigating the error. I've narrowed it down to if the Pinterest button is enabled in the Sharing section. If disabled, it does not throw the error and does show the other sharing buttons properly.

I did a fix and it worked on my local machine, but throws an error on your site. I'm going to need to set up a PHP 8 local site to step through this, as I haven't narrowed down whether it's a Joomla 4 change or a PHP 8 change that is causing different behavior than expected. I'll get there....

-Melissa

I was able to reproduce the error on a PHP8/J4 local site. I installed a fixed opengraph -content plugin on your site. I've re-disabled the JFBCContent plugin, so turn it on and clear your caching when you want the buttons to show up.

Also in Share/Content Plugin - Like if I select in Category Setting - Include and mark categories where i want buttons to apear I am not sure if selected categories stay remmebered after marking them to show buttons.

I'm not sure I understand what you mean by this. In the backend, if I select Include All and a category and then change any of the options for the Like buttons, the settings remain.
If you mean the changes aren't taking effect on the front-end: One thing that I've noticed is that you have Caching on in the Global Configuration area and also the System Page Cache plugin. If you want any changes to take effect on the front-end, then you'll have to disable and/or clear the cache first.

-Melissa