Over a billion people have taken them without significant problems. Probably way more than any trial for any treatment before or well into the future.
It is very hard to find this number. I know a person who got bad reaction to the vaccine, heart and brain aches. Their doctor turned them down, saying "that's normal, that's what vaccine does" a didn't even do ECG. How many people got treated this way?
Even if the rate of people having these long covid-like symptoms is lower than that of people who get covid it's still not riskless even though the risks are lower.
citation needed
Let us know what and where you're reading about these vaccine-induced long covid symptoms