Center sidebar content

you can add Custom CSS.

For example, elilyjay.com, add this custom css:

#secondary.widget-area { text-align: center; }

refer: https://www.wpbeginner.com/plugins/how-to-easily-add-custom-css-to-your-wordpress-site/

Thanks, this worked!

Is there any chance I could center images and other widgets too as well as text?

you can apply CSS to images and other widgets
Text widget with visual editor can easily center contents