So...
what "mythic lore" of lizardmen? I know of exactly
one actual human myth that involves explicit lizard-men, that being Egypt's Sobek, who has a crocodile head. I know of a handful of
science-fiction stories, but outright myths? Little to nothing. By comparison, dragon-people are MUCH better-supported by myth and legend. You have:
- Greek: the Spartoi, the "Sown Ones," who spontaneously arose from planted dragon's teeth in two myths, first Cadmus (where five of the Spartoi survived the "cast a stone amongst them to set them off" gambit, and they joined with him to found the city of Thebes) and later Jason on his quest for the Golden Fleece (though in that story they all kill one another.)
- Greek: the Ophiogenes, literally "Serpent-Born," who are descended from--wait for it--the Drakon Ophiogeneikos, "Dragon of the Serpent-Born." The dragon is also called the Mysian Dragon for where it kept its lair. Some versions of the myth have them descend from a woman who was herself the daughter of a drakaina, Sybaris.
- Greek: Humanoid "drakaina" (female form of drakon, lit. "dragoness") mate with several heroes, intending to produce royal lineages; Herakles is persuaded to sleep with one such drakaina, said to have created the line of kings of Scythia.
- Greek: Erichthonios, the autochthonous founder-king of Athens, is sometimes called "half-human, half-snake," but in others is explicitly referred to as being half drakon specifically.
- Chinese: The "Dragon Kings," frequently depicted as humans/humanoid. Asian dragons in general are usually able to take human form and sire human(oid) offspring, which usually gives the child special powers.
- Chinese: Shenlong, ruler of weather and rain, explicitly a dragon but also sometimes a person.
- Chinese: The Yellow Emperor, who is also the Yellow(/Gold) Dragon of the Center, and ruler of the cosmos.
- Mesoamerican: Quetzalcoatl was both a feathered serpent and, at least in some cultures, a human(oid) figure. The feathered serpent is a lot closer to a dragon with feathered wings than it is to a snake, at least IMO.
- Wendish/NW Slavic: Zirnitra, their god of sorcery, was legit a straight-up dragon, but also a person. I recently dug up the original text reference for this (having to pass it through Google Translate because I can't read Danish), and yeah. "Zirnitra" had such enormous importance for sorcery stuff, his very name became the epithet for "person who can use powerful magic."
There are a handful of vaguely "lizardmen" type things, though usually more in the form of
serpent people (e.g. the Aztec god Tlaloc, the Chinese creator-goddess Nuwa and sometimes her similarly-snaky husband Fu Xi, the Greco-Roman deity Glykon, Egypt's Wadjet is sometimes serpentine, etc.) The only "lizard" man I know of is, as noted, Sobek.
Dragonborn have tons of mythic support. The only thing they
don't have is tons of "written in the 20th century" fiction support. That's not myth--it's just modern fiction.