I travelled to Canada during this pandemic. My husband is a Temporary skilled worker here and I was stuck in the UK. I contacted the Canadian Embassy to get a Travel Exemption letter, however, if I had it all over again, I wouldn't have travelled.
In the UK I was able to work and earn money, whereas, when I landed in Canada I applied for Spousal Open Work Permit at the airport, which I couldn't get because my travel exemption letter stated that the purpose of me travelling was to "reunite with my husband" and not to work. So I was issued with a 6 months visitor visa and told to apply for SOWP online. I have done that but with biometrics closed, I haven't been able to get work visa yet. It has been nearly 4 months with no income for me, which is very frustrating, especially as we found Canada to be more expensive than the UK.
You can't apply for SOWP at the airport. That was never an option even before coivid. I think there was a miscommunication. Your inability to work has nothing to do with your letter. You would have always had to apply online for the SOWP. It could also take longer than 4 months.