On Thursday, May 13, 2021 at 1:01:18 PM UTC-4, Na'ilah wrote:
Found weird chalky off white build up blocking 1/4-1/3 of the toilet drain pipe - clinging to the rear wall of the pipe thicker at the flange and tapering to nothing at the elbow (about 10 inches down) - think it may be lime scale. It was causing toilet to flush strangely (swirling bits of TP left over) and clog frequently requiring plunging. I scraped it out, and I am about to put a new flange in.. hoping for the best, but thinking hard water/metal flange may be the issue. Toilet was put in about 25-30 years ago, so it was a slow process.

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Yeah, that's not lime scale. Not that thick, and not that easy to scrape.

Here's my guess. You had some repairs done, either dry wall or paint or both, and the contractor took a short cut and dumped drywall mud or something similar down there when he was cleaning up.