My current elaborate glyph imbuer cannot be used with either of my weapons - the fusion button is greyed out. Both weapons have an intricate glyph slotted. The imbuer can be used with talismans with intricate glyphs.
I might be able to unslot the glyph and upgrade it, but this seems like a bug and I’m a little worried that if I try that I might discover I can’t slot it into the weapon afterwards. Other people report being able to upgrade weapon glyphs to elaborate before, so this might be either specific to certain weapons or a recently-introduced bug.