Rear brake cable temporary fix possible? (Please see edit below; problem might actually be with brake lever)

I'd like to know if a temporary resolution is possible for my stuck rear brake cable.



Video:
https://drive.google.com/file/d/1EmGB78BphkK4k27j4BNouMpIK31A31ST/view?usp=sharing

I'm taking it into the shop but the soonest they can take my bike is Tuesday.  I have no experience in bicycle repair.  The bike is only half a year old, but I've been riding it in winter.  I clean the brakes (excluding the pads) every one or two weeks with a soft bottle brush and diluted dish soap. I have never lubricated any brake parts yet, though.

Edit: I might have been wrong on the location of the malfunction. The brake lever seemed stuck, and I assumed that was because the brake was stuck, but after squeezing it very hard it seems to work to some extent. It makes a creaking noise and doesn't move as freely or with as much range as the front brake.

Edit 2: The problem was the cable or housing, not the brake lever.
From the video, it looks like the cable has frayed inside the outer housing or something like that. I doubt there's anything you can do except get the bike shop to replace the cable.

Although most of the braking comes from the front brake, I woudln't recommend riding the bike in this state: you'd have no back-up if anything went wrong with the front brake.