Help Android phone is low on storage even though I have no third party apps.

[Shwath]

I have a Samsung Galaxy Express 3, and it has 8 GB of storage.
Recently I tried download a third-party app, but the Play Store told me I have no storage.
When I went to the storage menu and tried to figure out the possible cause, I was stumped when I saw this:

It says I have 3.81 GB in Apps even though I've uninstalled all of my third-party apps.
When I went through my list of apps, I counted and it seems like I only have 400 MB of apps.

In fact, the largest app is the 228 MB, so I have absolutely no Idea where the other 3.4 GB is coming from.

I used the DiskUsage app to try to see if I could find anything else, and now I'm even more confused. As shown in the picture above, System data seems to take up a lot of space. I'm not sure what this is since I was under the impression that all the System memory was stored separately, not in the storage card. I've tried using SD Maid and ES File Finder to search for any unneeded files, and they only removed about 15 MB in total. I'm not particularly tech savvy, so is it possible for someone to tell me what that system data is, and if/how I can remove it?

 

[svim]

8GB is simply not enough storage space for a modern, Android phone. You're either just accept your Express 3 has serious limitations and restrict what you do with it, or be prepared to take steps, on a very frequent basis (probably daily, maybe weekly), to do temporary, stopgap steps to free up a few MBs.
I'd recommend giving some serious thought into just switching to a newer, more capable phone. You don't need to budget a flagship model either, there are several really usable models in the $100-300 range for carrier unlocked models and under $100 for carrier branded models.
https://thewirecutter.com/reviews/best-budget-android-phone/
You shouldn't have to get frustrated each time you pick up your phone to use it. Get a phone that will just do what your need it to, there's no permanent fix for your low storage problem. You're always going to be fighting with it just to do every-day tasks.

 

[Shwath]

8GB is simply not enough storage space for a modern, Android phone. You're either just accept your Express 3 has serious limitations and restrict what you do with it, or be prepared to take steps, on a very frequent basis (probably daily, maybe weekly), to do temporary, stopgap steps to free up a few MBs.
I'd recommend giving some serious thought into just switching to a newer, more capable phone. You don't need to budget a flagship model either, there are several really usable models in the $100-300 range for carrier unlocked models and under $100 for carrier branded models.
https://thewirecutter.com/reviews/best-budget-android-phone/
You shouldn't have to get frustrated each time you pick up your phone to use it. Get a phone that will just do what your need it to, there's no permanent fix for your low storage problem. You're always going to be fighting with it just to do every-day tasks.

I'm definitely considering that, the only reason I ask is because I used to have an app that was 2 GB, but I deleted it, and now I can't even install an app that's 600 MB, so I'm trying to figure out where the issue is there.

 

[Dannydet]

Factory reset and start from scratch

 

[Hadron]

Those "system data" could be data stored by system apps? Maybe have a look at how much data (including cache) your aps aps storing.

(I considered that they might be updates to system apps, since these also live in the data partition, but DiskUsage on my phone shows those as "apps").