Is there any ways to set "Open in Teams" as default when user click an excel link?

Jimmy1116 Yes, there is a way to open excel file inside Teams. You need to modify the URL of the excel link into below format.

Ex: if your file URL is "https://my-url/someexcelfile/"

Step 1: Replare "/" with "~2F" in the ULR 

update URL should look like : "https:~2F~2Fmy-url~2Fsomeexcelfile~2F"

Step 2: Create team viewer URL with below format.

https://teams.microsoft.com/_#/<File-Type>/viewer/teams/<updated-URL>

Final URL should look like

https://teams.microsoft.com/_#/xlsx/viewer/teams/https:~2F~2Fmy-url~2Fsomeexcelfile~2F

This URL works for other file format as well. For viewing PDF file, you can replace "xlsx" with "pdf" and update the URL for pdf file.

Hope it helps.