Can't change text through customizer

When I click my title or any other textfield in customizer, it opens the new tab to fill in the text but doesn’t display any words. I cannot type or change anything.

I added a picture to verify my problem. Did anyone else experience this or do you have any idea how I could fix this?
If I can’t change it through customizer, is there any other way to do so?

Hey there,
I hope you’re doing well today

The image you’re trying to sent didn’t come through, as it is too large.

However as a solution to your problem you can use the following plugin to find and replace text on your website.

Best Regards,
Support

Hey,

I would prefer to get the old way working, to be honest.
Overhere you can see the image I tried to upload.

Best regards.