Non-profit organizations, educational institutions, and governments are exempt from the fee. The full policy is here: https://developer.apple.com/support/core-technology-fee/

If you don’t plan to charge for it, you can also just publish through the existing App Store infrastructure, where there is no fee.

(I’m not being an apologist. There are so, so many shitty things about Apple’s implementation here, but this isn’t one. I believe the EU should blast Apple as hard as legally possible for the rest of their implementation which is intentionally terrible.)