import { TabBar, convertNavigationProps } from "neumorphic-tab";

...

 <Tab.Navigator
        

          // The TabBar component is mean to be used in this property, there you can customize as you want
          tabBar={(props) => (
            <TabBar
              invert
              
              // convertNavigationProps is a function used to adapt this library with the navigation props. 
              {...convertNavigationProps(props)}
              
              // The properties below are optional, there are default values.
              itemColor={theme.colors.primary}
              focusedColor={theme.colors.onBackground}
              unfocusedColor={theme.colors.onSurfaceDisabled}
              textColor={theme.colors.onBackground}
              tabBarColor={theme.colors.backgroundSecondary}
            />
          )}
        >
          <Tab.Screen
            name="Pomodoro"
            component={PomodoroScreen}
            options={{
              tabBarLabel: ({ focused, color }) => (
                <Text variant="titleMedium" style={{ color }}>
                  Pomodoro
                </Text>
              ),
              tabBarIcon: ({ focused, color, size }) => (
                <MaterialCommunityIcons
                  size={size}
                  name="timer"
                  color={color}
                  focused={focused}
                />
              ),
            }}
          />

          ...

        </Tab.Navigator>

Example expo 51 app 

./src/_layout.tsx


import { Tabs } from 'expo-router';
import React from 'react';

import { TabBarIcon } from '@/components/navigation/TabBarIcon';
import { Colors } from '@/constants/Colors';
import { useColorScheme } from '@/hooks/useColorScheme';

// This line is need to be added
import { TabBar , convertNavigationProps} from 'neumorphic-tab';

export default function TabLayout() {
  const colorScheme = useColorScheme();

  return (
    <Tabs
      // These lines are need to be added
      tabBar={(props)=>{
        return <TabBar 
        {...convertNavigationProps(props)}
        // Customization props could be added here
        />}}
      screenOptions={{
        tabBarActiveTintColor: Colors[colorScheme ?? 'light'].tint,
        headerShown: false,
      }}>
      <Tabs.Screen
        name="index"
        options={{
          title: 'Home',
          tabBarIcon: ({ color, focused }) => (
            <TabBarIcon name={focused ? 'home' : 'home-outline'} color={color} />
          ),
        }}
      />
      <Tabs.Screen
        name="explore"
        options={{
          title: 'Explore',
          tabBarIcon: ({ color, focused }) => (
            <TabBarIcon name={focused ? 'code-slash' : 'code-slash-outline'} color={color} />
          ),
        }}
      />
    </Tabs>
  );
}