NOTE: This is the response I posted to your similar post on another thread. In it you gave 4230 as your model number.
Just so we're all on the same page, your Roku 3 (model 4230 is a Roku 3) will function just fine without a microSD card. All that a microSD card will do is increase the onboard storage for apps.
When you go to your Main Menu and you see all those apps listed, you need to keep in mind that they are apps that are on your account, not necessarily on that Roku device. The Roku 3 has only 256 MB of on-board storage. What it will do is download the apps as you use them, but when storage gets full, it will try to remove the app with the longest time since use and then download the one you're trying to watch. The message is letting you know that you can increase the on-board storage by adding a microSD card.
The Roku devices will only support 2 GB of storage from a microSD card. If you get one any larger, it will still only use 2 GB. In fact, if you get one too large, it may not even be able to read it, and problems could develop. Even if you get a microSD card, you've increased the app storage nine-fold, and while that's a lot, it's not infinite. If you have enough different apps that you watch, you could fill it up and still end up downloading apps each time you want to watch something. The chances are reduced greatly, but not fully eliminated.
The other thing about your situation is that you're running a Roku 3. I'm a huge fan of the Roku 3. It's been a great device and a rock solid performer for eight years, as model 4200 was introduced in 2013. Model 4230 was introduced in 2015, and has performed well for six years. You may have purchased yours later, but the 4230 was discontinued in later 2016, so it's been nearly five years.
It appears as if your device does not have a microSD card, since you're getting that message. I'm suggesting you don't worry about it, but if you do want to add one, don't get a large one. Anything over 2 GB is a waste. If you can't find one that small, get the smallest you can.
If that's the only issue you're having, keep using the Roku 3 until it gives out, but do keep in mind that your device is old in the timeline of streaming devices. Old, but still going strong (hopefully). It will give out one day, but I'd ride that pony as long as it could go.
DBDukes
Roku Community Streaming Expert
Note: I am not a Roku employee.
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