Multi-region US / EU / UK / AU for a fishing-tackle brand, Magento native?

Yes, via Magento Multi-Source Inventory (MSI), native since 2.3.0. The architecture for fishing tackle:

• Sources per region, us_warehouse (Florida or Tennessee for ground-shipping reach), uk_warehouse (England for UK + IE), eu_warehouse (Netherlands or Germany for EU bloc), au_warehouse (Sydney or Melbourne for Australia + NZ).
• Stocks per region, UK stock = uk_warehouse only; EU stock = eu_warehouse only; US stock = us_warehouse only; AU stock = au_warehouse only. Brand territory rules layer on top, some Sage SKUs are US-only and don’t appear in EU/UK/AU stocks.
• Store views per region, EUR/VAT-included in EU, GBP/VAT-included in UK, USD/tax-excluded in US, AUD/GST-included in AU. Same SKUs, different price visibility, different checkout (Klarna in EU, Clearpay in UK, Affirm in US, Afterpay in AU).
• Regional brand portals, Daiwa UK and Daiwa US are separate dealer agreements with different SKU catalogs. Source-level visibility rules keep each market clean.

Shopify Markets is similar but shares the catalog; you can’t easily hide a SKU per market without scripting. Magento handles it natively.