What has changed recently to potentially cause this? The COVID vaccine, plain and simple. You don't need exhaustive studies nor to spend millions of dollars to come to a correct conclusion. Court cases are decided "beyond a reasonable doubt"; they are rarely, if ever, "proven" scientifically. In fact, outside of mathematics, no scientific methods ever actually "prove" anything. There will always be uncertainty. Demanding "proof" is what an unreasonable person does; or a person with an ulterior, and potentially sinister, motive.

The fact that Occam's razor exists demonstrates how unnecessary and unattainable true "proofs" are in everyday life. We should always be open to new information and we should scrutinize everything with a healthy amount of discernment; but to demand proof where none can be attained is to ignore truth, facts, and reality. This is not something an intelligent, nor reasonable, person is in the habit of doing.