How do I get a strawberry?

I understand that I need a strawberry...

for the homunculus (vase), after starting a crusade in Lamascus, to complete some part of tricking the devil.

However, I have no idea how to get it. I got someone to start a horticultural school, but that doesn't seem to produce a strawberry.

How do I get a strawberry?

It seems that you have to learn about the strawberry from Kloc the skeleton in the dungeon. That, in itself, is a really gnarly puzzle, which you can read about in this guide.

Here, you should meet a skeleton named Kloc. Don’t run away! Choose “Attack” and he’ll talk to you instead. He’s a friendly skeleton who just wants some strawberries. Swipe right for everything and then he’ll let you leave the dungeon.

Now, everything can continue with the Homonculus and the machine in Lamascus.

You don't (or rather your character doesn't) understand that you need a strawberry.

You find out that you need a strawberry...

by talking to Kloc the Skeleton in his room in the Dungeon

You find out how to get there...

by solving the "years" riddle

Then to actually get the strawberry...

after the homunculus or the Lamascian princess takes you to the alchemical device, say you want a strawberry.