From the inside, in real-time, the modern view that the Roman Empire was a dictatorship was probably not all that apparent to your typical Roman citizen. If you stopped a Roman on the street and asked if he lived in a republic he would probably say “yes”. He might actually believe it, or maybe just fear arrest if he said otherwise.
Augustus Caesar decreed that the republic was restored shortly after he came to power. The Roman Senate continued to be elected for more than 500 years. Ironically, the Roman Senate actually regained some power after the Fall of Rome. The new Goth rulers accrued credibility by supporting the Senate.
Nazi Germany retained it’s elected assembly. (They did suspend elections for a while during the war.)
Most modern dictators retain that notion that they are ruling in a democracy. Some operate on the Trump Principle: If I lose then it must be fraud. They use martial law, corrupt courts. submissive elected assemblies, or militias, or some of all four, to restore democracy if they lose an election. And they make it hard or impossible for the opposition to win an election in the first place. And they neuter the representative assembly.
Basically, these are the principles of the modern Republican party in the USA.