So you are seeing HTML tags in surveys responses of your Feature Layer (like the below)?
There is no way to simply "remove" those HTML tags from there beyond editing the actual survey results in something like ArcPro.
I have dealt with this in the past when generating Feature Reports by using if() logic to replace the response that included HTML formatting with my own text since the if() statement looks at the name rather than the label. But that probably doesn't work on the web since the feature layer displays the label rather than the name.
Best practice would be to remove the HTML formatting from the survey and re-publish it. Then use ArcPro to modify the already published responses. Will make life easier in the long run.