When updating an extension (trigger or action) to a new version, the extension's old version will be in a deprecated status. It means the old version will remain usable for a few releases before getting removed.
Flows containing deprecated extensions will show a warning message advicing that flow contains deprecated extensions.
Flow detail will include a warning message on the specific deprecated extension.
It is recommended to update deprecated extensions to new versions. Once it is updated to the new version the warning message will dissapear.