People are buying my product. Conversion rate is low. But it's there. At what point I'll know with certainty that my idea is validated?

Congrats on the sales! Love following the journey of analogenie.

I think the validation process and success condition depends on your positioning and what your personal/business goals are for the business model you're creating.

Now that you're starting to get sales you can come up with a validation success condition based on where you want to take the business.

I recommend https://startupcalculator.co/ to help refine your goals

As an example for my company we switched our business model and pricing recently. We haven't validated the business model because we need more purchases to really understand the risks around what we offer HOWEVER we were able to validate our pricing by having current customers look at the pricing and get hype plus new customers have been coming on thanks to the pricing update

We've validated one aspect of our positioning; our price, but not the entire business model yet (problem, solution, marketing channels, etc)

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TL;DR
I'd ask yourself what your goals are with the project and set a validation condition based on your goals. Is it number of analogies generated? Is it a certain MRR where you know you want to work on the idea for another 1-2 years? Or is it a certain number of customers giving you feedback at a certain rate?

PS To answer your second questions "At what point I'll know it's worth working on the idea?" I think this is pretty personal and based on what you want but I'd say:

With 5-10 sales you should be able to start optimizing how you work and make money on the project (get customers, get feedback, update product)