That's a separate bridge.
Also, the Crimea rail bridge doesn't cut off Russia's southern army. It just cuts off the span between Russia and Crimea (city of Kerch) over the Kerch Straits (between the Azov and Black Seas). They still have the new land route between Russia, over southern Ukrainian territory that they just took, going through Mariupol and Melitopol to still get to Crimea and the rest of their southern army. That won't cut off anything except easy and direct access to Crimea (the bridge). They should still take that out though... but I think that is a separate and later campaign; only if and when the Ukrainians want to make an attempt to take back Crimea should they pull that move.
And I don't believe it's smart to go after Crimea either because Russia will unleash their full might and fury to protect the Naval Base in Sevastopol. Possibly nukes. They're not going to fuck around and lose Crimea. No. Possible. Way.
But in order for Ukraine to improve their bargaining power, significantly, they have to take back Kherson. Kherson controls the water supply into Crimea. 10 points. Kherson is west of Crimea, and west over the Dnieper (I think they spell it Dnipro) River. If the Ukrainians destroy THAT bridge, they strand 15,000 Russian soldiers west of the Dnieper River, with a dismal possibility of resupplying those soldiers, or their retreat. And facing Ukraine's full "western" campaign to take back that territory. I think those 15,000 Russian soldiers, once the bridge is destroyed and they can't retreat or get resupplied, surrender. 1 point (Putin could give a fuck how many soldiers he loses...). It also puts them in a position to easily win all the territory west of Crimea... and if they reach the land bridge leading into Crimea, they can easily block access into Crimea from the Donbas/ Russia/ Mariupol/ Melitopol highway. 100 points.
Now that rail bridge over the Kerch Straits COUNTS.