There is no upgrade option to reminders Mac

This will explain the situation.

https://support.apple.com/en-us/HT210220

Since you upgraded your iPhone Reminders, you will have to wait until macOS Catalina is released.

I just ran into this today. This is incredibly lame that they'd release a feature without having a corresponding way to access it on the Mac. I use it on my Mac for work stuff since it's easier to see on the Mac and put in URLs than on my phone.

Agreed, I have been totally p'd off!! I can't believe this is coming from Apple. I did gloss over that note about Reminders upgrade during iOS 13 upgrade on my iPhone yes but still? Reminders on iCloud is a joke as I can't order them chronologically there, can't create or edit reminders. Did we just go back in time? (I could edit them previously, even though I did not have much of need to do so. But now that I have the need to edit / add reminders due to the whole upgrade fiasco / horrible planning by Apple, I would have at least liked to be able to edit reminders there but nope.). Half of my reminders that have dates on my iPhone don't have any on iCloud!! Again this is a shame it's coming from Apple.

It should still show if you log into icloud.com, but do agree.