As realms are Mojang's Official servers I don't likely think they will so only resourcepacks, datapacks (early official modding api stages I see them as), worlds and maybe others that are official things Mojang allows support for will likely work. I don't own a realm though so I can only speculate if it's even possible now or the extent of plugins/admin control you get now but if it is possible then try installing Forge or Fabric onto a 1.14.4 Realms world.
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'Niche Community Content Finder' for fun and support of creators. I look for mods that interest me or need a bit of acknowledgement or bug fix testing/reporting. I also make modpacks/maps
Creator/Maintainer of Fabric, Rift & Tesla Mod Discussion Threads/Niche Mod Youtuber.