From the attached study, it appears low thyroid function can cause low testosterone which may be why most of us think its low T causing our symptoms when in fact, very well could be low thyroid function and probably both.
https://www.ncbi.nlm.nih.gov/pubmed/15142373
Its well known in the 60's and 70's our salt contained iodine and our drinking water did not have fluoride in it. Our great medical system decided to change all that and look what has happened since then.
Here is another great explanation of the link between thyroid and testosterone. Well written and easy to read.
https://www.restartmed.com/thyroid-symptoms-men/