There is no waiver and there is not likely to be one. There is no way to 'apply' for a waiver or any other sort of exception in advance of returning to Canada. After the point where you are out of Canada for 1095 days (five years minus the 730 day residency obligation), you will be non-compliant and may face issues entering and limitations such as not being able to sponsor family members or renew PR card. (At entry you can be reported for non-compliance and the process started to revoke PR status).
They are required to consider circumstances why you are not compliant, and may be lenient (at border or subsequently on appeal). While appeal is in process, a PR can remain in Canada and work.
While the system has some flexibility for compelling reasons to not meet the residency obligation (true humanitarian and compassionate considerations), make no mistake - PR status is intended for those residing in Canada, and the leniency allowed not really intended for broad "it would be more convenient for me to continue to reside abroad" reasons.
So the suggestion/feedback is: if you wish to retain status and permanently reside in Canada, it is better to return before your September 2021 date. (Note that if you are well short, you may face practical limitations travelling abroad until you are back in compliance, with some risk at each entry into Canada)
(Of course I have no idea about the specifics of your situation, these are general comments - there are many other threads on this topic)