No, puberty blockers are not 100% reversible and they are not harmless, either. Surgeries are not rare, either - at least it is debatable what should be considered "rare".
As to the real risks, time and again it has been shown that the comparative risks of a) receiving puberty blockers vs b) growing up a gender you do not feel you are, strongly points to puberty blockers being a significant net benefit. Those taking puberty blockers rarely regret it; whereas those growing up a gender they do not identify with mostly regret it are are significantly more prone to abuse, mental health issues and suicide.
The issue here is manipulation of children. If children were fed tons of harmful pain blockers, there would be a "panic", too.
It's because acetaminophen is extremely hepatotoxic at levels not very far above the recommended dosages.
> Hepatic injury and subsequent hepatic failure due to both intentional and non-intentional overdose of acetaminophen (APAP) has affected patients for decades, and [...] remains a global issue; in the United States, in particular, it accounts for more than 50% of overdose-related acute liver failure and approximately 20% of the liver transplant cases.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4913076/
I would assert that acetaminophen is far more likely to be dangerous to far more children than puberty blockers and yet I don't see any moral panic over children's Tylenol.
https://chiro.org/pediatrics/ABSTRACTS/Acetaminophen.shtml
Is that enough? And by the way this is a higher rate the abortion pill that was banned.