Most likely soldered. Can you get to it from below (basement or crawlspace)? If so, you may be able to just cut the closet bend pipe off and replace all with plastic (PVC or ABS) and connect it with a no=hub connector.
You should be able to just get a repair flange without having to remove the old one. Check with a hardware or big box store for the right parts.
You will need to use Tapcons in the concrete to secure it. Get the bit and Tapcons for that too while you're getting the repair parts.
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