We have different phones with different versions so I'm not sure if this is what you're trying to stop from happening.
When I type in an alphanumeric string using decimals it converts it to a website address. It not only adds the blue underline in blue but also turns the text to blue. If it's a numeric sequence it converts it to a phone number. Both are now links or shortcuts.
It's really annoying at times and I haven't found a way to stop it from doing that. It seems to react to a certain number of characters along with decimals spaces and no spaces. It would be a nice option to turn this off until we're actually adding a link to a website or phone number.
Galaxy S9 SM-G960U
Security Patch Level
December 1st , 2019