I was going to bring my 2020 Pacifica to a Dealer to have the transmission fluid changed. They said that they would flush it. Is that safe?
Only do a drain and refill; don't do a flush.
Also, for anything other than warranty or recall work avoid dealerships; find a trusted independent mechanic.
See below: That vehicle uses the ZF 9-speed (948TE) also used in the Chrysler 200 (video within link below is for 200 but also applies to the Pacifica; do drain and fill only (change/service filter if applicable); also you want to add the same amount of fluid that is drained out)
https://www.pacificaforums.com/threads/zf9-speed-transmission-oil-change-diy.40401/
Those transmissions were weak so I would actually drain and fill (service filter if applicable) no more than every 30,000 miles. And baby that transmission to get more life out of it.
The dangers of an ATF flush ....
(tech "forgot" to reconnect the lines. Transmission is toast)