WiFi issues on X98 mini

Hello everyone, I installed latest CoreELEC 21.0 on the X98 mini. The system itself works without any problems, but I have a trouble with WiFi. It’s impossible even to watch IPTV without endless stutters, if I’m trying to do something via SSH I can’t type a command properly, I was downloading a theme for 20 MINUTES. How to fix that issue? There was no such problems on 20.1, there are no such problems on Android either

Some system information:
WiFi adapter: AM7256
DTB: s4_s905w2_4g
iw says 120 megabits if I point into wlan0
Here is the iperf output:

homicidetv:~ # iperf -c ping.online.net
------------------------------------------------------------      Client connecting to ping.online.net, TCP port 5001
TCP window size: 16.0 KByte (default)                             ------------------------------------------------------------
[  1] local port 52968 connected with port 5001 (icwnd/mss/irtt=14/1448/89248)                              [ ID] Interval       Transfer     Bandwidth
[  1] 0.0000-20.1343 sec  2.13 MBytes   885 Kbits/sec