Croatia
Registered as an obrt, taxed on profit-share as self-employment income. Under the lump-sum (paušalni) regime only 15% of revenue is the tax base, so the effective burden is ~11-13% of gross for revenue under EUR 60,000.
Self-employment income from a registered trade (obrt) - business income, not capital gains.
Lump-sum obrt (paušalni): taxed on 15% of revenue (85% deemed expenses), then ~20-30% PIT on that base = low effective rate; income-method obrt taxed at 20-30% on net profit.
Mandatory pension + health; for lump-sum obrt these are flat monthly amounts (~EUR 200-300/month total).
Register an obrt; lump-sum option up to EUR 60,000 annual revenue, otherwise income-based bookkeeping; annual return.
USDC is taxable self-employment revenue in EUR at receipt; later crypto disposals are taxed separately (generally as capital income if held).