Will Starlink's internet speed degrade as the number of users increases?

Yes, theoretically that's the case, and this trend has actually been observed.

It's not complicated; I'll give you an analogy to make it clear.

Imagine it as a Highway

Satellites = Highway Lanes: Each Starlink satellite in orbit can be thought of as a highway for data transmission. Its total width (how many cars can drive on it simultaneously) is limited; this is what's technically referred to as "bandwidth."
Your Internet Usage = You Driving: When you stream videos, play games, or have video conferences, these data packets are like cars speeding down the highway.
Number of Users = Traffic Volume on the Road

Now the situation is clear:

When there are few users: The entire highway has only a few cars (yours) driving on it. The road is wide and straight, so you can drive as fast as you want, naturally experiencing "blazing fast" speeds. This is why early Starlink users enjoyed extremely high internet speeds.
When there are many users: When hundreds or thousands of users in the same area try to access the internet at the same time (e.g., during peak evening hours), it's like thousands of cars flooding the same section of the highway. The road is still as wide, but with more cars, congestion is inevitable, and everyone's speed will have to decrease.

This is what's called "network congestion," and it's the same principle as your home Wi-Fi slowing down when too many devices are connected, or your phone's 4G/5G speed dropping during peak hours. Every user is competing for the limited satellite bandwidth resources.

Starlink's Countermeasures

Of course, Elon Musk is aware of this issue, so SpaceX has been doing several things to alleviate congestion:

Aggressively launching new satellites: This is the most direct method, equivalent to continuously widening the highway, or even building entirely new highway networks. The more satellites there are, the greater the total available bandwidth, and the more users can be served simultaneously.
Upgrading satellite technology: Newer generation satellites (like V2 satellites) have greater capacity and higher transmission efficiency than older ones. This is like upgrading a 4-lane road to an 8-lane road and also increasing the speed limit.
Optimizing network scheduling: Intelligently allocating and scheduling network resources to ensure more efficient data transmission and minimize "traffic jams."

In Summary

So, yes, Starlink's internet speed will slow down as the number of users increases, especially in densely populated areas. Your actual experience depends on the user density in your area and how many satellites are serving you at that moment.

However, thanks to SpaceX's powerful satellite deployment capabilities, it is striving to make the speed of "road construction" outpace the speed of "car buying" to maintain a relatively good user experience. But the laws of physics cannot be broken; the nature of shared resources dictates that speed fluctuations are an inevitable phenomenon.