No LTE on samsung s4 mini? I am using a Samsung S4 Mini Model GT-l9195 with Lineage OS 14.1. I used the LTE Image to install LOS. But actually, I am not sure if my phone is able to use LTE. Because there was also a non-LTE version available for LOS, I wonder if there are Samsung S4 phones that don't have LTE built in?

The problem is, I have never seen the LTE sing with the mobile data icon yet, but I am also not using Internet very much on the phone.
As you already know, LineageOS explicitly offers different ROMs for the 3 variants: serrano3gxx (GT-I9190, 3G single-SIM), serranodsdd (GT-I9192, 3G dual-SIM) and serranoltexx (GT-I9195, LTE single-SIM).

The assert checks embedded within the packages will prevent them from being flashed on the wrong variant of device, but this is given that you installed the correct recovery for your variant as well (for which there are no similar assert checks).

With the correct ROM and recovery, if you're still not getting LTE, you should try forcing LTE in Settings. Also be aware that the device itself is a rather early LTE device and as such has very limited LTE band support; PhoneDB shows support for only LTE B3/B7/B20. If your carrier doesn't use any of these bands then naturally you won't get LTE whatsoever.