Does Ravenbloom Conservatory force me to recycle the card if it's not a spell?

Yes, Ravenbloom Conservatory does force you to recycle the card if it is not a spell.

According to the card's ability:

"When you defend here, reveal the top card of your Main Deck. If it's a spell, put it in your hand. Otherwise, recycle it."

In Riftbound, "Otherwise" functions as a mandatory instruction for any card that does not meet the "If" criteria (in this case, being a spell). Since Units and Gear are not Spells, they must be recycled.

According to Rule 403.2.a:

"The player must Recycle cards from the specified zones when instructed to do so by game effects or costs."

Because the effect uses the word "recycle" rather than "you may recycle," the action is mandatory. You take the revealed card and put it on the bottom of your Main Deck (Rule 403.1.a).