This error usually occurs when some plugins and/or the WordPress version isn’t updated.
Can you try and make sure all the plugins are fully updated and WordPress itself is updated as well?
Note: Some plugins may still not work if if their last update wasn’t tested to WordPress version 5.8 because there was a big change with how the Widgets were placed. WP 5.8 turned widgets into blocks. 😀
A wise man once said:
"Have you cleared your cache?"