Removing all plugins is a drastic method to fix a simple problem. (Which is why I gave that answer a downvote.)
The error messages indicate a problem with a specific plugin. You can rename or delete the folder for that plugin. Renaming the plugin’s folder will disable it. Removing the plugin’s folder will disable it without possibility to recover.
So, as the other person mentioned in their answer, the problem doesn’t appear to be in the theme, but in the plugin causing the error message.
If the plugin’s features are important to you, you could try reinstalling the plugin’s files via an FTP from the latest version of the plugin that you download. Or you could rename the plugin’s folder and reinstall it.
But removing/deleting all plugins to fix a problem is like taking a giant Thor hammer to put a nail in the wall for a picture. Rename the entire wp-content/plugins folder to something else to temporarily disable all plugins, then copy individual plugins folder into a newly created wp-content/plugins folder to re-enable that plugin to check if that plugin is causing the error.
But, a careful reading of the error message will usually point in the direction to go. Use the ‘scalpel of renaming things, rather than the “Thor’s Hammer” of a massive deletion of all plugins.