Flutter singlechildscrollview fixed TextField

You could try putting your TextField outside your Scroll widget, removing the unnecesary SingleChildScrollView, and replacing the scroll physics in your ListView:

    Widget build(BuildContext context) { 
    final localStorage = GetStorage();
    
    return Scaffold(
      appBar: HomePageAppBar(),
      drawer: HomePageNavigationDrawer(localStorage),
      body: Column(
              children: [
                TextField(
                  onChanged: (value) => _runFilter(value),
                  decoration: InputDecoration(
                    contentPadding: const EdgeInsets.symmetric(
                        vertical: 10.0, horizontal: 10.0),
                    hintText: "Search",
                    suffixIcon: const Icon(Icons.search),
                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(20.0),
                      borderSide: const BorderSide(),
                    ),
                  ),
                ),
                ListView.builder(
                  physics: const BouncingScrollPhysics(),
                  scrollDirection: Axis.vertical,
                  shrinkWrap: true,
                  itemCount: _allUsers.length,
                  itemBuilder: (context, index) => Card(
                    elevation: 1,
                    margin: const EdgeInsets.symmetric(vertical: 2),
                    child: ListTile(
                      title: Text(_allUsers[index]['name']),
                      subtitle: Text('${_allUsers[index]["generic"]}'),
                    ),
                  ),
                ),
              ],
            ),
      bottomNavigationBar: const HomePageBottomNavigation(),
    );