Hi,
According to your description, my understanding is that you want to filter a lookup column in Calendar list by latest value.
There is no OOB way to achieve your requirement. As a workaround, you could create a new column to judge whether the lookup column is created last using JavaScript. If yes, set the value of the judge column current time, and then filter items by the judge
column.
About how to retrieve list items using JavaScript for your reference:
https://msdn.microsoft.com/en-us/library/office/hh185007(v=office.14).aspx
About how to update list items using JavaScript for your reference:
https://msdn.microsoft.com/en-us/library/office/hh185011%28v=office.14%29.aspx?f=255&MSPPError=-2147217396
You could insert a Content Editor Web Part in the page and add code in it. About how to use Content Editor Web Part:
https://support.office.com/en-ca/article/Content-Editor-Web-Part-c1350ff6-934c-4c2e-8e53-1ec3b548a0dc
Thanks,
Dean Wang