Now in Microsoft Teams we can define the default option to open files within the client. To change that setting, just open the Settings dialog in the Teams client, scroll down to Files section and choose the option you want to use:
Once you select the desired option, it will show up as default option to open a selected file in a given channel. Note that from here you can change at any point the open file option.
Same behavior happens when we make use of the “…” next to the file name to display the file options. Clicking on “Open” will show same file open options identifying the default one configured. Of course, if you click the file it will immediately open using the option configured.