You can do this by Deep linking - https://docs.microsoft.com/en-us/microsoftteams/platform/concepts/deep-links#deep-linking-to-a-chat.
But this is unsatisfactory because the link doesn't take you directly into a chat in Teams; it takes you to a confusing launcher page that your average user will give up on.
Sort this out - https://microsoftteams.uservoice.com/forums/555103-public/suggestions/31308418-deep-links and we'd be happy.
Teams Deep links go to a terrible launcher page atm. This is so user unfriendly. They should open intelligently; in desktop Teams if it is installed and available or in a browser window if not.
At present deep links are unusable because of this. Those of us programming apps using ms graph need this to use deep links. This is essential for creating apps that use Teams.
Please do this. At present deep links only work within Teams. Otherwise the user gets a confusing launcher page, which negates the use totally.
Allowing deep links to work without going through the launcher is essential for those of us programming applications using graph