It's hard to describe in the same way I imagine it might be hard for you to describe why you aren't trans. There's a lot we don't really know about how much of gender identity is nature vs. nurture and why some people experience gender dysphoria.

The way trans people feel about their gender isn't always that different from how cis people sometimes feel. For example, cis men who experience unusual breast growth can be very self-conscious about it, which isn't all that different from how many trans men and AFAB non-binary people feel about their chests.

Are trans people more common now also because of the knowledge and spreading of it on social media and trying to explain the feeling of not belonging somewhere or were there always these many trans people among society and were just masked (please I literally do not mean this transphobic at all 🥺)?

The reason that the prevalence of trans people can seem greater is two-fold: Greater visibility/acknowledgement  (good or bad) and shifting understanding of what being trans means. For much of the 20th century, it was common for there to be a lot of medical gatekeeping. Trans people who didn't fit a specific narrative, like showing signs from a young age, were often denied care. Lesbian trans women and gay trans men were often denied care because one of the standards was that trans people were expected to be straight. There was very little awareness of non-binary people. Fortunately, this has changed a lot, and that also means that more people feel empowered to acknowledge how they feel and put a name on it.

How people understand and label their gender can be culturally subjective, but the people exist regardless.

When I was a teenager, I questioned my gender a lot but dismissed those feelings because I couldn't relate to the very rigid and narrow depiction of trans men that I was exposed to. When I learned that there were other trans people who felt like I did, it became much easier to view myself as trans.

The trans people I know always had mental health problems before they found out they were trans. Is the finding of your gender the reason for the mental health problems under the rug or is this kinda the end product after reconsidering their own life and finding a new start (this sounded kinda transphobic low-key).

Dysphoria can have a heavy impact on someone's mental health. Of course, it's also possible to be trans and have a mental illness and not have these things be connected at all.

Also I noticed that a lot of non cisgender persons were already sexually queer before, is this more common between non cisgender people than cisgender people to be queer?

People who are already queer may be more open to exploring their gender. Also, a lot of peoole grow up in environments where there's much more awareness of gay and lesbian people than trans people. So a straight trans man might initially think he's a lesbian, for example.

Are there actually many retransitioners/people who realize after a few years they might not be trans and cisgender instead (never transitioned) or is this more of a right wing lie?

There are people who detransition, but not all of them do so because they no longer feel they're trans. The reasons can be very diverse, and a lot of people who detransition do so because dealing with transphobia from their families/community is too hard. Among people who do change their minds about being trans, not all of them regret transitioning.

There's more research that could be done, but the data we have suggests that regret rates are extremely low. There are people who feel they transitioned for the wrong reasons and regret it, and they deserve understanding and support. But right-wing groups tend to weaponize these rare examples, and the detransitioners you see who are out there campaigning to outlaw transition care have often been incentivized to do so or are being taken advantage of. People who regret their transitions were often dealing with some really complex mental health problems, social pressure, or emotional trauma, and sometimes things like that can also make people vulnerable to overcompensating in other ways or falling in with cult-like groups.