Dioxygenase that demethylates RNA by oxidative demethylation: specifically demethylates N(6)-methyladenosine (m6A) RNA, the most prevalent internal modification of messenger RNA (mRNA) in higher eukaryotes (PubMed:29180595). ALKBH10B-mediated mRNA m6A demethylation stabilizes the mRNA of the key flowering time regulators FT, SPL3 and SPL9, which are involved in the control of floral transition (PubMed:29180595). 2-oxoglutarate + an N(6)-methyladenosine in mRNA + O2 = an adenosine in mRNA + CO2 + formaldehyde + succinate Binds 1 Fe(2+) ion per subunit. Reduced vegetative growth and late flowering. Belongs to the alkB family.