New Teams - Set most recent app view as default

Workaround:

Create a Windows shortcut and use the command line arguments for MsTeams to target the desired module.

1) New > Shortcut
2) Type the location of the item

msteams:/l/[TARGET]

3) Valid targets can be Calendar, Channel, Entity, Meetup-Join, Chat-Join, and probably others yet to be discovered 

msteams:/l/calendar

msteams:/l/channel/[CHANNEL ID]

msteams:/l/entity/[ID of another target such as a Plan]

To get a Microsoft Teams channel ID from the app, navigate to the desired channel, click the three dots (...) next to the channel name, and select "Get link to channel" from the menu. A popup will appear containing a link; copy this link. The channel ID is the string of characters that appears in the URL immediately after /channel/ and before the next slash. For example, in the URL https://teams.microsoft.com/l/channel/19:0b0d1aae685345b28bcc9dda9010cc94@thread.skype/Support%20Channel?groupId=..., the channel ID is 19:0b0d1aae685345b28bcc9dda9010cc94@thread.skype.

When copying the link, the channel ID may appear with URL encoding (e.g., 19%3a...%40thread.skype). If you need to use the ID in APIs or other systems, replace %3a with : and %40 with @. This method works in both the Microsoft Teams desktop application and the web version at https://teams.microsoft.com/

UPDATE:

I also discovered that by copying the link to a Planner "Plan", it's also possible to launch Teams directly to open that plan. This uses the "entity" target. I haven't experimented extensively but "entity" might also work to target other things. Open a Planner tab or the Planner App (within Teams), choose "Copy Link to Plan", then take the part of the URL that begins with "entity/" and put that as the launch target for msteams:/l/

NOTE:

"msteams:/l/" (with the target after the second slash) is the complete command. It is not necessary to locate teams.exe or provide a path to the executable. "msteams:" is a native shell command that invokes the program. 

I don't care about meetup-join or chat-join, but you can read about it here:
https://ananthasharma.medium.com/how-to-open-ms-teams-meeting-from-command-line-terminal-ea501f6dd6ca