Because Dass Anand is not a Unicode font, text typed in this font will not be searchable on the web and will appear as random symbols if you copy-paste it into a modern browser or smartphone. You must use it within desktop publishing software (like Adobe InDesign, CorelDRAW, or Microsoft Word with the font embedded).
If you are looking for modern, Unicode-compliant Tamil fonts that are pre-installed or easily accessible for web and professional use, consider: dass anand tamil font better download link
How to Instal Tamil Fonts (FREE) in Windows 10/11 Using Microsoft Store Because Dass Anand is not a Unicode font,