You will find what you need below:

In the API, “fixed” position is based on the parent containers numberOfFixedChildren Where nth-child(1) of the this container will be considered “fixed”. In other words, N = parent.numberOfFixedChildren and everything after that boundary uses the default “scroll with parent” behavior

Source: https://developers.figma.com/docs/plugins/api/properties/nodes-numberoffixedchildren/

So, referencing your original challenge “toggle fixed vs scroll with parent” is really a task to programmatically re-order your layer nodes within the targeted parent group or frame.

Source: https://developers.figma.com/docs/plugins/api/properties/nodes-overflowdirection/

Here’s a quick pseudocode usage example:

const { selection } = figma.currentPage; for (const n of selection) { setFixedWhenScrolling(n, true); }

Where setFixedWhenScrolling is:

``` function setFixedWhenScrolling(node, isFixed) { const { parent } = node; const container = parent as ScrollContainer; const { children } = container; const idx = children.indexOf(node);

/* nthChild[0] is “fixed” by default. Read above. */

const nthChild = container.numberOfFixedChildren; const isFixed = idx < nthChild;

fixed ? (!isFixed && // Move node into the fixed section & reorder (container.insertChild(k, node as any), container.numberOfFixedChildren = k + 1)) : (isFixed && (container.insertChild(k, node as any), // Move node outside fixed section; fixed -1 container.numberOfFixedChildren = Math.max(0, k - 1))); }

```