Voting machines are bad. Their use makes it easier to commit fraud. However, those claiming fraud in the 2020 elections claimed "absolute proof" of fraud (Mike Lindell, the MyPillow guy's, words) when they were demonstrably bluffing.
It is both the case that voting machines can be compromised and that we know the most well-advertised claims of election fraud in the 2020 election are themselves fraudulent.
If you're talking about experts in voting systems, no they didn't. Trump's CISA appointee to oversee election security, Chris Krebs, claimed the election was highly secure, which in a sense it was, because Trump had long been advertising concerns about the election which stimulated election security efforts. But in security you can never be completely sure the attacker doesn't have some trick you haven't thought of, so nobody competent claimed absolute proof of no fraud.
It is both the case that voting machines can be compromised and that we know the most well-advertised claims of election fraud in the 2020 election are themselves fraudulent.
https://blog.erratasec.com/2021/11/example-forensicating-mes...