Greetings, samanthafromwarrnambool.
I see that your iPhone 8 Plus isn't vibrating when you expect it. Good job on the troubleshooting you've used, and I'm happy to help.
How to put your iPhone on vibrate, ring, or silent mode -- Toggle the Ring/Silent switch to see if you feel a vibration. Also check Settings > Sounds & Haptics > Ringtone and check "Vibration" at the top to make sure the vibration you've selected is long enough. You should also feel the vibration as you tap each one.
Also check Settings > General > Accessibility > Vibration to make sure it's turned on.
Update your iPhone, iPad, or iPod touch -- Make sure your iPhone is up-to-date. You can check Settings > General > Software Update to confirm if your iPhone is on iOS 12.
Let me know how that goes, and take care!