Dear AppSheet Community,
I just found a nice trick if you work with the Microsoft environment on your computer.
I share it here if that helps someone.
This is under Behavior > Actions, as you may have guessed 
Do this: “External: go to a website”
Target:
"https://teams.microsoft.com/l/chat/0/0?users="&[useremail_target]
EDIT:
Another one, thanks to @SkrOYC 's Tip : this is for creating a meeting schedule, with one-hour duration, starting from now, ending one hour later.
I improved it thanks to @SkrOYC 's suggestion:
CONCATENATE(
"https://teams.microsoft.com/l/meeting/new",
"?subject=", ENCODEURL([Subject]),
"&content=", ENCODEURL([Content]),
"&startTime=", ENCODEURL(TEXT(NOW(), "MM/DD/YYYY HH:MM:SS")),
"&endTime=", ENCODEURL(TEXT(NOW()+"001:00:00", "MM/DD/YYYY HH:MM:SS")),
"&attendees=", USEREMAIL(), ",", SUBSTITUTE([EmailList], " ", ""),
)
it makes the expression free from any date formatting issue.
If anyone has a suggestion to add to this thread, please feel free to comment!