Widget breaking the site

I like what this plugin offers, but I am running into a problem. I used the shortcode in a text widget, and in order to get that to work I had to add this to functions.php:

add_filter( 'widget_text', 'do_shortcode', 11);

Unfortunately, when I added that it also broke the site partially so CSS was clearly off. When I removed the add_filter line, the site appeared normally, but the widget then only showed the shortcode text rather than the Youtube output.

I then tried using the actual Auto Last Youtube widget rather than using shortcode, but this simply broke my site like it had when I used the shortcode and add_filter code.

Any sense of what is going wrong here? Thanks in advance.

https://www.ads-software.com/plugins/auto-last-youtube-video/