Insignia™ NS-50F501NA26 50” Class F50 Series LED 4K UHD Smart Fire TV

According to the user manual, the USB port can display .jpg files but given that this TV has FireOS (Android) Install it is likely that you can do video and install APK files from the USB as well. Not if you want to get access to the file system you may need to download Total Commander or ES File Explorer to install APK files from the USB Port. Also make sure the USB stick uses the FAT32 format to insure compatibility.

How to Format a USB Stick to FAT32 Using Windows