Connection to new router not possible

Hi, I need some help:

Today I got a new "lte router" (it uses the mobile internet, which is many times faster than the conventional internet that I used before). My girlfriend's Windows PC is perfectly connected, as is my smartphone (original Iphone SE) and my tablet (an iPad).

My laptop with Slackware current also connects via Ethernet without any problems, but not via WiFi. I am using NetworkManager and when I try to connect through nmtui I get asked for a password multiple times. At the end it will say that a password is required but not given. When I try to connect through nmcli and provide the password as an argument, it times out after a while. I've already tried not to set a password at all, but then it expires after 90 seconds with no successful connection.

I've tried almost every possible combination of settings in the router, but couldn't find a solution. Here are the settings right now:

SIM card status:
SIM card ready
Connection status:
Connected
Network name:

Network type:
LTE
Profile name:
congstar Internet
IPv4 address:
10.163.165.24
IPv6 address:
2a01:598:b889:b8e3:65a3:ed5d:8105:76e6
Cell ID:
26546947
RSRQ:
-10 dB
RSRP:
-110 dBm
SINR:
-110 dB
PLMN:
26201
Network mode:
Auto
Connection mode:
Auto
Automatically connect even when in roaming:
On
Profile name:
congstar Internet (Default)

Wi-Fi 2.4GHz:
On
SSID:
congstarMoritz
Country/Region:
Germany
Security:
WPA2
Encryption:
AES
Wi-Fi password:
its a string of numbers, so this should not be the problem

Ah, I almost forgot an important detail: this is the only network where I can't connect to with my laptop, no problems with other wifi networks