It is common knowledge in the osteoporosis community and frequently discussed on another forum, Inspire, where a doctor has input.

Googling brings many sites on this:
https://www.osteopenia3.com/Strontium-dexa-scan.html
https://www.inspire.com/groups/bone-health-and-osteoporosis/discussion/effect-of-strontium-on-dexa-score/
There are also health risks with strontium, which led the European Union to withdraw the ranelate from from the market. Strontium is not regulated in the US. Some brands, like Doctors Best, have discontinued it after the health risks were discussed in Europe. Please read this on both the risks and the effect on DEXA.
https://americanbonehealth.org/medications-bone-health/why-strontium-is-not-advised-for-bone-health/
"Research from Europe suggests that patients on strontium ranelate may have an increased risk of heart attacks[1,3], blood clots,[1, 3] and serious skin reactions (DRESS syndrome)[3]."

This site also says “Strontium… results in an overestimation (up to 50%) of the increase in bone density using DXA methods.”[3]

Even after all this, I confess to thinking about using it after Tymlos if I cannot tolerate anything else. Not saying I would, and I am all for using regulated meds if tolerated, for osteoporosis severe enough to warrant meds. Strontium is no more "natural" than anything else and the citrate form has not been studied adequately, nor is it regulated.