Hello! Thanks for the additional info. :)
Were these folders on a Micro SD in your Samsung phone? If so, double-check that the size of the photos aren't too big to fit on your new iPhone.
You can check how much storage space your iPhone has by following these steps:
- Open Settings
- Tap General > Storage Space
If that isn't the problem, you may have to restart the set-up process on your iPhone: How to factory reset your iPhone, iPad, or iPod touch - Apple Support.
However, I understand that this can be an annoyance so you can also manually transfer your photos over to your iPhone using a computer:
1. Connect your Android to your computer and find your photos and videos. On most devices, you can find these files in DCIM > Camera. On a Mac, install Android File Transfer, open it, then go to DCIM > Camera.
2. Choose the photos and videos that you want to move and drag them to a folder on your computer.
3. Disconnect your Android and connect your iPhone, iPad or iPod touch to your computer.
4. On a Mac with macOS Catalina, open Finder. On a Mac with macOS Mojave or earlier, or on a PC, open iTunes. On your computer, sync your photos to your iPhone, iPad or iPod touch. You can find your photos and videos on your device in Photos > Albums.
(Move content manually from your Android device to your iPhone, iPad, or iPod touch - Apple Support)
Alternatively, using a third-party app such as Google Photos or DropBox should also be fine when transferring photos over to your iPhone.
Hope this helps!