Sure, they will probably don't give that fines, but they could, what if I run a small business that interferes with the activity of some other business run by for example someone that is friend or can corrupt the people in charge of doing the fines ? They will fine me for 20 million dollars, sure I can appeal, a normal trial in my country lasts at least 5 years, in this time I will probably go out of business...
The fact that they could it's a big problem, they should have specified a proportion between the size of your company and the maximum allowed fine.
But as I already said, the stability of the EU’s economy depends on fair application of the law. If the EU levies a 20 million Euro fine on a company with 20 million/year in revenue, the chilling effects of that action would cause much more than 20 million in damage to the EU economy. That should be blatantly obvious. Despite propaganda to the contrary, the EU has a very good record of behaving as a reasonable government entity, moreso than most. They’ve championed quite a few consumer-friendly pieces of legislation that have managed to not destroy the applicable sectors.
If you think this is a valid concern, I can only assume you’re just as worried about other outcomes that have insane, struck-by-lightning levels of unlikelihood, in which case you are not going to have the spare cycles to be able to successfully run a business anyway.
Tax code violations, for sure. Environmental regulations may also carry huge maximal fines. Some misdeeds can even lead to criminal prosecution and land you in jail (but generally, they won't, except for the worst of transgressions).
Note that the GDPR requires fines to be proportional to the offence. If you really worry about some regulator fining you for 20M euros just because they're having a bad day, you do have legal recourse available.