That ~1% figure is unlikely to reflect the full picture of regret. That paper defines regret very narrowly: only including the patients who made an appointment with their original medical team to discuss regret, and only if they regret surgical removal of their sex organs. Plus, a large number of their total cohort were lost to follow-up.
“The Amsterdam Cohort of Gender Dysphoria Study (1972–2015): Trends in Prevalence, Treatment, and Regrets” (DOI: 10.1016/j.jsxm.2018.01.016).
The word “many” is misleading – it’s less than 1 %. It’s not nothing, but it’s low.