Use arguably if you believe you could give reasons to support your opinion 🙂

There is a difference in usage. Your translator and some of the answers aren’t complete. ‘Arguable’ is used for questions that are interesting, controversial, debatable etc. Perhaps it will rain tomorrow. (Ok) Arguably it will rain tomorrow. (No) ‘Arguably’ isn’t inherently that certain and I would say that is more often used to propose a position that is a little surprising or controversial. We grew up hearing that Pele was the greatest soccer player of all time, but today he arguably doesn’t make the top 5. (I’m going to make this argument.) As someone else noted, ‘inarguable’ conveys certainty. ‘Arguable’ just says that there is a minimum level of evidence making the position reasonable.

You can use arguably when you are stating your opinion or belief, as a way of giving more authority to it.

Yes, it's a smarter sounding way to say 'probably. If you see the word 'inarguably' that means with a near absolute certainty.

It is similar to "probably" but a little bit more formal. "The year 2020 has arguably been the most surprising year of the century so far"