Instead, a regulation could mandate the administration an anonymized unbiased mandatory eval test at the end of every week/bi-week/month just like instruments for psych evaluation (e.g. do you feel your <mental-health-metric> has become worst in the last <time-period> on <scale>. Did you have <mental-health-marker> after watching content on social media?).

The said regulation can then mandate that after calibration and correction the feed pull back by training the algorithm to adjust it in a rapid A/B test.

This is all doable by the companies themselves, but since they wont, the key is to mandate it and publish the aggregate results regularly — like make it part of the quarterly share holder's SEC reporting requirement or something.