What are aspects to your world that would affect how your species approaches spaceflight?
For instance, a species with little to no navigable oceans or a fully aquatic species may find it difficult to develop the cultural skills necessary to run a ship because there isn't a tradition of operating a ship the same way there is for humans.
In my superhero setting, most alien species are able to find an alternate means to orbit around their corresponding Steam age, and can achieve interstellar flight by the time they've developed vacuum tubes. Most species also don't really have the superpowers humanity displays, our rate of technological advancement, or have Defender guardians blockading their home system - although all these traits have co-occurred with a few other extinct species known to the local intersteller empire.
As a result, humanity is largely confined to Earth; we have our satellites and a few moon bases, and some efforts at a Mars colony, mostly backed by Reed Richards type super geniuses.
Sometimes aliens will slip through the Defender blockade; hoping to smuggle out (relatively) advanced human technology, or even superheros to sell. Generally Defenders will intercept these, but sometimes they'll slip through. And sometimes, humans will "acquire" their ship. Refugees from various interstellar incidents have also been allowed through a few times by the Defenders.
Humanity has so far been unable to work out how interstellar travel is achieved, but research continues. Every human-controlled interstellar ship has a story behind it, and most are the former property of interstellar slavers and smugglers. Some carry representatives of Earth governments and organizations interacting with their interstellar counterparts, and others are crewed by superhero teams who acquired a ship that was temporarily Earthside, or humans who overthrew their captors.
Why would other species be able to create interstellar ships before humanity? Is it a material that Earth doesn't have?
Also, if there are several interstellar species trying to learn from Earth, why wouldn't one accept a trade and research treaty of some type with Earth to gain access to human technology. If humanity is able to build a wall to repel alien contact, why wouldn't trade occur to give humanity access to interstellar travel in exchange for lesser human military hardware?
The Defenders have our solar system either blockaded or quarantined, depending on who you ask. This prevents extraterrestrial development of Earth, while our own developmental blind spot keeps us from developing our own FTL systems. Individuals can sometimes slip through, but they arrive in force at any hint of large scale fleet movements.
After the first few attempts to reverse engineer alien interstellar drives failed, neuroscientists, parapsychologists, and assorted mentalists began their own investigations. The current consensus is that the concept behind FTL travel is strangely slippery for the human psyche. Common alien concepts like "the folding song", "the scent of the spheres", and "ether stairs" are nonsensical to us, as if we're missing some critical frame of reference. Dr. Adrian Braums in 1968 went so far as to describe this as a "deliberate, species-wide incision", but her subsequent creation of the villain SnapStep has led many to discredit her. Without this crucial insight, we're left with brute-forcing our way out of our gravity well by chemical explosions, and other stars remain out of reach entirely for now.
As for the Defenders, they aren't human. We've always had our own larger than life heroes and villains, gods, demigods, giants, and monsters; but as near as we can tell, the Defenders started paying attention to Earth around 1200-1800 years ago. From records recovered from (non-Defender) alien craft, recollections from alien visitors, and two interviews with Defenders themselves, we know they're an interstellar group of fantastically powerful, insular individuals who typically intervene in planetary scale and larger crises - evacuating planets ahead of supernovas, redirecting rogue black holes from populated systems, etc.
When they first arrived at Earth, they declared it under quarantine, and began intercepting ships attempting to land here. When Yuri Gagarin first made it into orbit, the Defender Oo'Oblansk welcomed him aboard his own vessel; this encounter was only recently declassified, and details remain unavailable beyond it being a "friendly chat". However, vessels from outside our solar system are strongly discouraged, outside of a few rare cases (the Memm refugees being a recent example).
The Defenders have also been implicated in disabling at least one captured FTL vessel that was being outfitted for a human led expedition; they have not revealed their reasons for doing so. However, when interviewed by the BBC in 1984, Oo'Oblansk strongly denied that the Defenders had anything to do with our inability to comprehend FTL travel.
As near as we can tell, there is usually one Defender stationed at Sol system at any given time. They seem to rotate out every decade or so. We've confirmed one other species that the Defenders have blockaded/quarantined in this way; the home planet of the now extinct Krennesek, who also exhibited a wide range of physical abilities and rapid technological progress without interstellar travel. Their planet exploded in 966 CE.
If a species is arboreal (like my yinrih) many may choose to live permanently in microgravity to allow them to use all of those prehensile extremities for prehending instead of walking.
Also consider the reasons why a species pursued spaceflight in the first place. Humans were using it as a show of power. Rockets are just fancy missiles, after all. The yinrih pursued it for religious reasons, meaning that people who died while furthering that goal are venerated as literal martyrs.
Why would the yinrih pursue rocketry for religious reasons? Was there a drive to levitate themselves literally?
Thus said the Uncreated Light:
[1]: A nonsapient species of vulpithecin closely related to the yinrih [2]: Refers to the yinrih's primordial written language, developed from a scent-marking behavior simultaneously with a spoken language. As such, the yinrih have a written history that stretches back to the dawn of sapience in their species, roughly contemporaneous with the advent of behavioral modernity in humans on Earth. [3]: "The fire of understanding", or the faculties of language and symbolic thought [4]: to meditate on the mysteries of Creation, or to undertake scientific research, is regarded as an act of worship, and the accrual of knowledge plays an important role in Claravian eschatology.