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Below is a picture of two Continental 5000's that were kept in their boxes for about two years:
They were kept out of direct sunlight inside a house that was not climate controlled.
The tires feel very flimsy and don't seem to hold form.
Is it safe to ride these tires on a 200+ mile bicycle ride?
I would have no qualms about using those tires. I agree with Paul H in the comments that I would not use any new equipment for the first time in a big event—it always needs a shakedown.
Tires can degrade in storage, but that degradation should be visible, in the form of cracks in the rubber. I've got a pair of Conti GP 5000s that I rode for a while, removed, and have hung in my un-conditioned garage for over a year. They look fine to me.
I'll also mention as an aside that back in the old days, there was a myth that aging tubular tires improved them.
A GP5000 tire is flimsy and doesn't hold form. The reason is that they unfortunately are available only in Kevlar bead form.
Long time ago, you had a choice between steel and Kevlar bead. The idea was that your main tires had steel bead, you used them for their ease of installation and cheaper price. Then if you went on a long tour, you brought one Kevlar bead spare tire with you. The Kevlar bead tire compresses to a smaller size so it's easy to carry it in a small bag as a spare tire.
Unfortunately, with weight weenies being as common as they are today, the high-end steel beaded tires disappeared and today it's all Kevlar bead if you want to buy a slick road tire with a low rolling resistance. That disappearance of steel-beaded tires made fixing punctures so hard that today people are making various strange inventions to avoid fixing punctures, like replacing the time-tested inner tube with a slimy fluid that expires in less than a year, and requires certain compatible rims and rim tape, making all of your existing stock of rims and rim tape obsolete.
Two years of storage is fine. I had bike tires bought in 2009 or 2010 (don't remember which year exactly), and after a break for cycling resumed using them in summer 2020, although quite rapidly I replaced them with better tires (they were UltraGatorSkin and I replaced them with GP5000 -- not because 10 year old tires would be very unsafe but because GP5000 has much lower rolling resistance).
In car tires, the usual rule of thumb is that if you have a tire that's older than 6 years, you don't install it to a rim. If you have a tire that's older than 10 years, you remove it from use and replace it with a new tire. I have used on a car little-driven 22 years old studded winter tires, they had poor traction but still plenty of tread depth. On a bike used in winter I wouldn't do the same because the consequences of lost traction are more severe on a bike than on a car.
But 2 years... that's like yesterday. By all means, use them!
