This problem is still not solved as of November 9, 2019.
Samsung_avWoubd posted his solution which is to click on a button in the top left of the messages list. There is no button on top left, only top right. He then said to click on advanced settings, but there is no advanced button in the options.
I was able to find a button in the settings under "more settings" called "enable web previews".. but I had already disabled this many months ago, yet the day/date link bug/feature is still happening. I tried enabling and disabling "enable web link preview" and this still does not solve this problem at all. "Enable web link preview" allows you to see a simple screenshot of a website URL. It does not affect the messages app auto generating calendar links when you type words like "today, tomorrow, 3pm, 11:15am, etc...".
We need an actual solution as this is still an unsolved problem.