Dental fillings are supposed to follow the original contour lines of your tooth to imitate the natural form of your tooth. If done so, the fillings should have no problems staying put after clear aligners have been placed on it. Fillings done in an unnatural manner may lead to extra pressure on your clear aligners, which will exert the same force back to the fillings and may cause them to weaken their grip on the tooth in the long run. This will mean that your fillings will have a solid chance of falling out, so be aware of this if you have such fillings and want to get clear aligners. This would also possibly mean that your fillings were done in an unprofessional manner, which might lead to other problems with clear aligners. That being said, clear aligners breaking teeth should not be a problem. This only applies for fillings.
An unprofessional dental filling might not have a very tight grip on your teeth, which may cause the force clear aligners exert on them to be simply too much. Fillings might come out under such circumstances and should be considered when getting clear aligners on your fillings or vice versa. Bad dental fillings might not immediately come out under normal circumstances, but will eventually fall. One should not get bad fillings in the first place, and if they have, should consider getting them redone with better materials or by a better dentist. You might also want to read about getting clear aligners on gum recession