You Probably Can't Do This
The meaning of "prepared spell" can be confusing: like "attack" or "action", it is a term with flexible meaning in English, but also a fixed technical meaning in the game. Usually, it means a spell which is selected by members of certain classes at the end of a long rest, and is thus available throughout the day to be cast via spell slots. At first glance, this implies that spells cast via Magic Items are not "prepared spells."
But this is complicated by the fact that Glyph of Warding is on the Bard's spell list, but Bards do not "prepare" their spells in the sense stated above. So you might think that "prepared" spells could apply to any spell you are ready to cast.
That being said, a notable distinction is drawn between spells that are "prepared" and cast from a magic item on page 201 of the PHB.
Known and Prepared Spells: Before a spellcaster can use a spell, he or she must have the spell firmly fixed in mind, or must have access to the spell in a magic item. Members of a few classes, including bards and sorcerers, have a limited list of spells they know that are always fixed in mind. The same thing is true of many magic-using monsters. Other spellcasters, such as clerics and wizards, undergo a process of preparing spells. This process varies for different classes, as detailed in their descriptions.
In every case, the number of spells a caster can have fixed in mind at any given time depends on the character’s level.
In this text, we see that spells which are "prepared" are "fixed in mind." We also see that spells which are "fixed in mind" and spells cast through a magic item are two different categories.
Although this doesn't settle the debate definitively, it does highly imply that spells cast through a magic item are in a separate category than those which are "prepared." And since Spell Scrolls are considered a Magic Item (DMG, p. 200), it is likely that spells cast via their use could not be stored in a Glyph of Warding.
Naturally, your DM will have to make a ruling. They could be convinced that the "prepared" term in Glyph of Warding's description refers to how the Glyph "prepares" the spell to be cast when triggered. Or maybe they might just figure that Glyph of Warding already takes so much planning and foresight to use (an hour of casting and 200 gp in materials) that it won't make too much difference if you expand its use to spells cast via magic items.
The rules don't lay out an unambiguous path, so each DM will need to decide. But the only guidance laid out in the rules does suggest that your proposed strategy is unlikely to work.