SwiftUI: List cells flicker during scroll when .searchPresentationToolbarBehavior(.avoidHidingContent) is used with searchable modifier inside a sheet (iOS 26)

Description

When a searchable List is presented inside a sheet and uses .searchPresentationToolbarBehavior(.avoidHidingContent) to keep the navigation bar visible during search, the list cells flicker/blink under the keyboard

This reproduces with public SwiftUI API only — no UIKit, no appearance-proxy customization.

Steps to Reproduce

1. Create a new iOS App (SwiftUI) project (deployment target iOS 17.1+).
2. Replace the generated App file with the sample code below.
3. Run on iOS 26 (reproduces on both device and Simulator).
4. Tap "Open transfer methods" to present the sheet.
5. Tap the search field so the keyboard is shown (search becomes active).
6. Scroll the list down, then up into the top bounce (overscroll)
7. Observe the cells under the keyboard.

Expected

Cells scroll smoothly under the keyboard; no flicker.

Actual

Cells under the keyboard flicker/blink during top overscroll. See the attachments with shots of the process: 1. screen before a blink, 2. Screen in the moment of blinking

Sample Code

import SwiftUI

    @main
    struct FlickerReproApp: App {
        var body: some Scene {
            WindowGroup { RootView() }
        }
    }

    struct RootView: View {
        @State private var isSheetPresented = false

        var body: some View {
            Button("Open transfer methods") {
                isSheetPresented = true
            }
            .sheet(isPresented: $isSheetPresented) {
                NavigationStack {
                    SimpleSearchScreen()
                }
            }
        }
    }

    struct SimpleSearchScreen: View {
        @State private var searchText = ""

        private let items = (0..<40).map { "Recipient \($0)" }

        private var filteredItems: [String] {
            searchText.isEmpty
                ? items
                : items.filter { $0.localizedCaseInsensitiveContains(searchText) }
        }

        var body: some View {
            List {
                ForEach(filteredItems, id: \.self) { item in
                    Text(item)
                }
            }
            .listStyle(.plain)
            .navigationTitle("Transfer methods")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .topBarLeading) {
                    Button("Close", systemImage: "xmark") {}
                }
            }
            .searchable(text: $searchText, placement: .automatic, prompt: "Search")
            // Remove the line below -> flicker disappears, but the navigation bar
            // (title + toolbar items) then hides during search, which we need to keep.
            .searchPresentationToolbarBehavior(.avoidHidingContent)
        }
    }

Notes / What was ruled out

• Removing .searchPresentationToolbarBehavior(.avoidHidingContent) eliminates the flicker — but then the navigation bar hides during search, which is exactly the behavior the modifier is meant to prevent.
• Presenting the same screen NOT inside a sheet does not flicker — the sheet presentation is required to reproduce.
• Independent of app-level customization: reproduces with no UINavigationBar/UITabBar/UISearchBar appearance proxies and no UIKit.
• Also tried, did NOT help: .scrollEdgeEffectStyle(.hard, for: .all), .toolbarBackground(.hidden, for: .navigationBar), keeping the bar visible via UISearchController.hidesNavigationBarDuringPresentation = false instead, .geometryGroup() on rows, .scrollDismissesKeyboard(.never), removing safe area insets.