Most of my experience building hypothetical societies comes from worldbuilding for my D&D setting, but I've discovered interesting things about what works well from seeing my players interact with the different political parties and countries I populated the world with.
My number one important point to follow is that no matter how much you, as a person hate a particular political system you've put in your world, you will never make it believable unless you can assume the role of a person who totally believes in it for purposes of writing or, in D&D, improv performance.
For example, I've played characters like a highly conservative dwarven mayor who believes there ought to be military conscription, and argued very convincingly that shouldn't the players, as daring adventurers, be allowed to keep all those treasures they found and not be taxed on them? (This was amazing because my players all consider themselves liberal and they haaaate this guy on principle, but they also don't like the idea of being taxed on their treasures, despite objectively being way better off than common people in their world, it was very entertaining.). I've also played NPCs from a kingdom ruled by a lich queen; they were very content with their lives, cheerfully telling players that, sure people sacrifice their souls to the lich, but they're criminals or willing volunteers, and in return the country has a stable, predictable, unchanging parliament made up of ghosts so you never need to think about politics, and skeletons to do the manual labour so the living don't have to!
In other words, you need to come up with really genuine, viable reasons why a person would think this governing was fine, and the reason can't be "I'm stupid", because it's clearly the case that plenty of people of average or above average intelligence can buy into systems that are awful from an outside perspective or when you think them through. An average person doesn't enjoy having to think about politics, and especially doesn't like when politics is in the way of their ability to just about fulfil the bottom of the pyramid of needs. You tend to get pushback on a system either when: A lot of people can't get shelter and food. OR a decent number of people are comfortable enough with their shelter and food and educated enough with enough time to think through the system and go "hang on a second..." If you have BOTH of these happening at the same time, well, hello, Revolution! You'll get the upper middle classes rallying the poor with catchy slogans and "look at the excesses of the ruling class! You deserve a better life!" and then heads start rolling. (The "excesses of the ruling class" can be anything. While in revolutionary France it was like... living in huge gold palaces and wearing fancy silk clothes that were in an entire stata above normal people's squalid lives, many modern conservatives frame things like being gay or nonbinary, or eating avocado toast as excesses of the effete "metropolitan elite" while hailing people who own million dollar yachts as "men of the people". It's really all in the advertising.)
The easiest way to get a feel for it is to think of what the "elevator pitch" for this governmental system is. Systems with a catchy, simple founding mythology tend to catch on better (which is why socialism is such a hard sell, it's complicated and relies on scientific facts that contradict common assumptions that seem logical). In Theocracies, it's usually a belief that governing a country is a big responsibility, best left to a divine being or pantheon with a greater plan, and hey awesome, these priests have been given the authority to speak on behalf of that divine being. All a person needs to do is get on with their life, follow the rules in the scriptures, go to the temple once a week. Everything is planned out, no arguing over what the law is or politics because they're handled by perfect, divine beings with far better judgement than a human and you get to go to paradise when you die.
Any problems with such a system can be blamed on a priest becoming corrupted by their imperfect human nature, and any criticism of it can be framed as criticism of perfect divine beings by an impudent upstart mortal, so it can have some staying power! ...BUT if the priests start acting in corrupt ways publicly too much, or too much is taken from the populace (ie. too much money, or other tithes of food etc.), or the rules make basic living inconvenient (ie. a religion that forbids eating a specific plant or animal faces a crisis where after a disaster that thing is one of the only things to eat.) and there's a refusal to relax or change the rules... well, you may get a revolution on your hands.
