Why does the ZTE MF823D Modem (not branded) with a white IP not give it to the Zyxel Keenetic router. How to solve the problem?

Question

network hardware

Friends! Here is such a problem! I'm wandering in three pines and I can't get out. So ... There is a ZTE MF823D modem with a white IP from TELE 2. By sticking it into the Zyxel Keenetic router, I get not a white IP on the router, but another one. In the modem settings, everything is in order. IP is white, but the modem does not want to give it to the router, it generates its own IP and gives it to the router. I saw some similar problems on the Internet. In particular, it was proposed to enable DMZ on the modem. In the modem settings, either because it is not branded, or for some reason I did not see the DMZ checkbox. There are no updates from ZTE for this modem. Fortunately, Zyxel allows the DMZ modem to be turned on directly on the router, I did it, but the problem remained. The ZTE MF823D modem does not want to give a white IP to the Zyxel Keenetic router? What to do? How to solve the issue? Help, please, to whom the situation is familiar.
PS Throwing out a modem to buy a new one is also being considered, but then I will be grateful for advice on which one to buy so that there is no such problem?