Hope you are doing well and sorry for the trouble. As described, you have a very large cursor and the highlight is in large ovals.
Is this a behavior with a particular PDF file or with all the PDFs? Please try with a different PDF file and check.
If the PDF file is scanned document, please try to run the OCR on the file and then try to highlight the text and see if that works, Open the PDF > Tools > Scan and OCR > Recognize Text > In this file.