There's likely some CSS on textarea inputs that'd be doing that. Switch to default Joomla protostar template and default CB profile template then purge Joomla cache and retest to see if the issue goes away. You can also try right clicking the input and clicking inspect element (or just inspect, depends on the browser) to open your browsers developer console at that element. From there you should see the HTML structure on the left with the textrea selected and the CSS for it on the right where you can review what CSS is setting a width on it. If still not able to find the issue you'll need to PM frontend login credentials and provide a URL to the issue where I can review the CSS.

Have reviewed your install and for some reason some JS on your site is removing form-control CSS class from elements. With that CSS class removed it loses most of its styling. Looks like it's coming from custom JS loaded by 3rd party CB template plugin jf_sirena_cb_20. Changing back to default CB template did not appear to solve the issue so that JS file is likely being loaded by some other means than by normal template loading and likely acting on a trigger to do so. Suggest contacting the developer of your template as they need to remove that JS.

Nope, you need to contact the developer of your Joomla and CB template. They need to remove that code. Specifically it's in the below JS file.

/components/com_comprofiler/plugin/templates/jf_sirena_cb_20/jf/assets/js/jf.min.js

For some reason your site is also loading what looks like same JS file from your other install CB template even though it's not being used. It can be found below.

/components/com_comprofiler/plugin/templates/jf_connecto_cb_20/jf/assets/js/jf.min.js