When I try to install the xiaomi.eu_multi_MI5SPlus_6.11.10_v8-6.0.zip, I get the following message:
Updater process ended with error:7
This package is for "natrium" devices; this is a "capricorn".
Capricorn is Mi5S not Mi5sPlus. How big is your screen? If it's 5.15" you do not have a plus. If you have 128GB, do you have 4GB RAM or 6GB RAM? If it's 4GB, you have a 5S. 5S Plus has 5.7" screen and 6GB RAM for the 128GB model.
That looks correct. For some reason there is something wrong with the recovery misidentifying your device or the file you are trying to flash. Have you tried flashing another natrium ROM? (either Chinese stable/developer or global from Xiaomi?) If that gives a similar error then re-flash your TWRP or even try to download the xiaomo.eu ROM again in case it was modified (the timestamp seems to indicate not though).