Dropping the centered FAB. Export is a one-off action, not a category, so it shouldn't sit in the middle of the navigation. Each phone keeps the tab bar for categories and gives download its own distinct button. Tap the download button in any phone → the export sheet (format + single/sheet) rises.
A clear ↓ Export button lives top-right in the toolbar — always visible, never scrolls away. The bottom bar is pure navigation (4 even tabs). Cleanest separation: navigate at the bottom, act at the top.
↓ Export in the toolbar · 4 even tabs below
The tab bar is plain category tabs; a distinct ↓ Export pill floats just above it, bottom-right. It reads as "the action," separate from the tabs, and stays put as you switch categories.
Floating ↓ Export pill · tabs full-width below
One bar, but split: category tabs on the left, a filled Export ↓ button anchored on the right. No floating element, and the primary action is unmistakably separate from navigation.
Tabs left · filled Export ↓ anchored right
My lean: A (header download) — the action is always visible and never fights the tabs; or C (split bar) if you want it bottom-reachable by thumb. All open the same export sheet (Single / Full-sheet · PDF / SVG / DXF).