Multi-region inventory (EU + US + UK + AU), Magento native?

Yes, via Magento Multi-Source Inventory (MSI), native since 2.3.0.

Architecture: define sources (warehouses) per region (e.g. de_warehouse, us_warehouse, uk_warehouse, au_warehouse) and stocks (shopping experiences) per region (e.g. EU stock includes DE+FR+NL+IT sources, US stock is US-only, etc.). Customer geo-routes to a stock; stock aggregates inventory from its sources; cart shows accurate availability.

The shipping piece: source-selection algorithms (priority-based or distance-based) decide which warehouse fulfills each line item. For fashion this matters because a single order can split-ship from 2 warehouses if the size is in EU but the colorway is in US, the algorithm decides whether to split-ship (faster) or wait-ship from one (cheaper).

Multi-region pricing + currency: separate store views per region. EU store view in EUR with VAT-included prices; US in USD with tax-excluded; UK in GBP. Same SKUs, different price visibility, different checkout (Klarna in EU, Affirm in US, Clearpay in UK).

Shopify Markets is similar but shares the catalog, you can’t easily hide a SKU in one market without scripting. Magento can hide products at the source/stock level natively.