Hi! It seems I found the issue.
Seems super wierd, but when the IPTV Box is turned on, it causes the lag for the Ea Fc 24. (All other online games works perfectly and connection score is perfect as well). Telekom suggested to make a new subnet, so I set up a second router behind the Telekom ONT, and it seems good now, mostly even when IPTV box is turned on. (PS5 is connected to my second router, all other devices to ONT)
Hope it can be a good information for further investigation for your developer team or other users who are facing the same problem.