lol I Guess Your Definition of realism is different then mine !
My realistic opinion is, I Don't Know Everything !
& Have Not physically toured and Mapped the Entire Earth.
so my Mind is Open
as For My definition of "Giant" Is not 8' , 9' Feet 12 Feet, I Suppose is Gigantic , However even that is Small enough to be possible today I Guess
A child Large enough to Build the Pyarimids with Toy Building block in the Sand ? would be a giant

But I guess the Dinosaurs ate them all
I Draw the line at Ghosts & Hocus-Pocus



But creature. I Say Possible
There are, and always have been, exceptionally tall individuals… about 29 verified from medical history who were at 8 feet tall or more.
https://en.wikipedia.org/wiki/List_of_tallest_people
But those people were not part of a giant group or population of giants. They were one-offs, usually arising from genetic issues such gigantism, Proteus syndrome, Marfan syndrome, benign tumour-induced acromegaly, and various diseases or malfunctions of the pituitary gland with consequential growth hormone disorders.
Typically, these disorders create health and mobility problems arising from the effects on skeletal anatomy. Robert Wadlow, the tallest ever person properly documented in medical history at 8 feet 11.1 inches, had little sensation in his legs or feet and needed leg braces to walk. He was diagnosed with hypertrophy of the pituitary gland at the age of 12, which might have been correctable by surgery, but his parents felt the operation to be too risky.
[Picture colourised, but not otherwise altered]
Wadlow died in 1940 and, a year before his death, he had surpassed the previous title-holder John Rogan who had been 8 feet nine inches at the time of his death in 1905. Rogan had pituitary gigantism compounded by ankylosis (severe joint stiffness and partial fusion of his skeleton). By the age of 15 he was unable to walk or stand and moved around in a cart pulled by goats.
[By r/OldSchoolCool -
CC BY-SA 2.5,
https://commons.wikimedia.org/w/index.php?curid=107695371]
The Ukrainian Leonid Stadnyk claimed to be 8 feet 5 inches, but photographic evidence suggests he was no taller than 7 feet 7 inches. He died in 2014 from a brain haemorrhage linked to the pituitary gland tumour driving his gigantism. For living people, Bao Xishun from China had been the tallest at 7 feet 9 inches from 2005 until 2009 when Sultan Kösen from Turkey surpassed him. Bao had served in the army and worked as labourer but, by the age of 40, was reliant on crutches and could not stand for long periods without a walking stick for support. He experienced an unusual natural growth spurt that began in his mid-teens, but has normal growth hormone levels and no diagnosed pathological condition. Kösen has gigantism and acromegaly caused by a tumour affecting his pituitary gland. He was a farmer and briefly played professional basketball but now, at the age of 43, he also needs crutches to walk although any further growth has been curtailed by medical intervention.
These kinds of mobility issues are entirely to be expected because of the limitations imposed by the ‘square-cube law’: the mathematical principle whereby an object’s volume and mass grow much faster than its associated surface area and structural strength. The former grow in proportion to the square of the size and the latter grow in proportion to its cube. So, for example, doubling an object's linear dimensions multiplies its surface area by a factor of 4, but multiplies its volume and weight by a factor of 8.
It’s (one of) the key reasons why giants (let’s say 12 or 15 feet tall) with a conventional humanoid anatomy and bipedal locomotion do not exist, and never could have existed as a healthy sustainable race or population. Unless you’re going to claim ‘aliens’ (ho-ho). It’s impossible for them to have legs which would support their weight. A human scaled up to that height would likely break its legs or crush its joints under the massive weight.
If giants ever did exist, they would have to exhibit a completely different anatomy and mode of locomotion. Gigantopithecus blacki, the largest known primate (which became extinct between about 295,000 - 215,000 years ago) might well have stood as much as 10 feet tall. There aren’t enough fossil bones to reconstruct the anatomy but, although once believed to be a hominin, it’s now classified in the subfamily Ponginae, along with modern orangutans. The consensus is that it had a sturdy gorilla-like stature, moving on all-fours and only occasionally standing upright.
Large animals such as elephants (and prehistoric ones such as sauropod dinosaurs) counteract these problems by being quadrupedal and/or having thick tree-trunk-like legs to distribute their weight.