given you seem to know them better than us would you kindly elaborate?
The D&D Dwarf shares almost zero in common with the various mentions of Dvergar across Norse texts.
In the Norse texts, the Dvergar are:
• Normal human size
• Personify the fates (nornir), especially a fate of failure and curses
• Powerful mages and makers of magic items
• Dvergar are highly knowledgeable and value knowledge (víss)
• Personify the patterns, rock shapes and mineral artwork, in rocks and mud
• Petrify into rock in direct sunlight − whence some of the rock shapes
The Dvergr is normal human size, in Norse texts and in Viking Period artwork that depict a human and a dvergar as the same size. One text even mentions a Dvergr having the height of a giant, "the body of a Thurs", tho the Norse giants themselves also are usually humansize despite the possibility of family members who reach extreme heights. Note, the Saxon Dwarf (British and German) is characteristically short, about half the size of a typical human. There is even a later Norse (Old Icelandic) translation of a German text in the 1400s, that mentions that this particular German Dwarf is unusually short, compared to the Norse Dvergar. If the D&D Dwarf is "Medium or Small", like the Human is, it is easy enough to mention that Dvergar can be any height, with various regional averages.
The famous three nornir are jǫtnar, who immigrated to become æsir sky beings relating to the cosmic tree. But there are masses of nornir, who determine the fates of individual humans. These many thousands of fate-speakers are Alfar and Dvergar. The Alfar correspond with speaking success, while the Dvergar with speaking the lack of it. But both Alfar and Dvergar are masters of any kind of magic. Sometimes the bad-luck Dvergr is referred to by the ironic nickname of a good-luck "Alfr". The Dvergar can grant helpful luck by means of cursing ones enemies.
For the D&D Dwarf to lack magic is non-Norse. There are Norse texts that explicitly identify Reginn as a Dvergr, such as the Dvergatal in the Vǫluspá. This is enough to establish that the concepts relating to Reginn correlate with concepts relating to the Dvergar. We see he masters shamanic magic, including shapeshifting into a dragon, and comes from a shamanic family who are also shapeshifters, such as into an otter and so on. The D&D Druid with its Earth elementalism and wildshape is appropriate for some Dvergr concepts. Various personal names relating to death and corpses refer to the deathlike trance of a shamanic who travels outofbody.
Also, Reginn repairs a broken magic sword. Dwarves elsewhere are also famous for creating some of the most powerful weapons in the cosmos, such as the hammer of Thórr, because of the fateful failure magic against the resistance to the weapon. So while Thórr is the son of the most powerful jótunn in the cosmos, his mother, and already has giant strength, his belt makes him effectively stronger than every other giant. In D&D, the Wizard with high Intelligence, expert knowledge, and making magic items can also apply to some Dvergar concepts. But a "spellbook" is never Norse. When later Norse texts refer to the magic grimoires from foreign nations, Norse uses its term "enchantment" galdr, from shamanic chanting, but reusing this term to cover generic magic including foreign magical methods. The Dvergar express kinds of magic that can be more powerful than the æsir. The æsir fear the dvergar and need the dvergar as allies.
The Dvergar across Norse texts relate to stone and mud (aurr). By definition the Dvergr live underground "in stones" away from direct sunlight.
The Dvergar petrify into stone while in direct sunlight, relates to the many humanlike patterns in rocks and mud. (In D&D terms, they take Radiant damage in direct sunlight, and when failing death saves at zero hit points, the corpse becomes stone.) Dvalinn is an ancestor of all Dvergar, whence the Dvergs need to avoid direct sunlight is poetically called "the game of Dvalinn" (dvalins leika). When the Dvergr Álvíss asks to marry the daughter of Thórr, implying her being buried alive, Thórr resolves the diplomatic consequences of spurning this Dvergr by distracting him with questions until the sun rises and petrifies the Dvergr into rock. The Reginn family mention shapeshifting into watery swimming creatures, whence humanlike and animallike shapes in river bed rock and mud.