I do not think every business needs an app. However I do believe a lot of businesses that do not have an app probably should have one.
I like to think about it like this: your customers are always on their phones. A mobile app is one more way to be there when they need help. They do not have to open a browser type your name into a search bar and hope they find your website.
That is the point. Everything else comes after that.
What you actually get from an app
Direct access. You do not have to worry about search bars or other browser tabs stealing attention. Your mobile app stays there on their home screen. A website just cannot compete with that kind of visibility.
Push notifications. A website cannot tap someone on the shoulder to say "your order is ready" or "here is 20% off today." A mobile app can do that. Most people allow these messages because they chose to download the app.
Offline access. Phone signals drop all the time. A good mobile app can keep working without internet. A mobile app can show saved content. Wait to finish a task until the signal comes back. A website mostly cannot do that.
Speed. A mobile app usually feels much faster than a website. This is because most of the app is already on the phone so it does not have to load everything from scratch every time someone taps a button.
Usage data you can actually use. If people say yes to it a mobile app gives you a look at how people use your product. You can see what they open and where they get stuck. It is much harder to get that kind of data from a website.
When it is probably not worth it yet
If most people visit your site once do one thing and never come back a good mobile website is better. Asking someone to download an app for just one thing is a big ask. Most people will not do it.
A mobile app makes sense once people start coming. If you have repeat visits or long-term tasks then the work of building an app starts to pay off.
The real question
It is not about "app or no app." You should ask: how often do your customers need you and what do they need from you?
If they need you regularly and need things fast a mobile app is probably worth the cost. If they only need you once in a while to look something up you do not need an app yet. A good website will do a job, than a mobile app that nobody uses.
You should make this choice based on how people use your business. Do not just assume every business needs an app.
If you are trying to figure out if you need an app lets talk about it.