iMac BigSur 11.4: how do I block Chrome from loading on start-up?

I have Chrome on my computer because one site I need to visit occasionally requires it. The rest of the time I do not need or want it. But it has somehow grabbed hold of my operating system and is the first app to install itself on boot up. And it takes a loooooooong time. Sometimes as much as 10 minutes. How can I stop that and get Safari to load as my browser of choice?