By 2021, Belgium has been annexed into the German Empire. The status of Belgium has not changed by 2162.
The Kingdom of Poland, the Kingdom of Belarus, and the Kingdom of Ukraine are still under German and Austro-Hungarian influence by 2021, and are closely allied politically with both Berlin and Vienna through the European Community and a network of mutual defense treaties.
Questions on the Eastern client states.
First Poland: Who got to rule Poland and to the present? Archduke Charles Stephen and his descendants? Also, how did Poland manage to prevent some of their territories being annexed by the Germans (whom had ulterior motives IOTL and planned to ethnically cleanse the Poles during WWI in the event of victory from annexed land), and how would the Oath Crisis have been solved? The Poles would protest such action and the victorious CP would not want to deal after tiredly winning the war, and so they give in to them IMO. I myself have thought of writing the idea out on Filling the Gaps and how it would have resulted.
On Belarus: Who rules them? IOTL there was the Belarussian Democratic Republic, which existed between the Treaty of Brest-Litovsk and the Soviet takeover. There was a mixed stance regarding them by the Germans, but as far as I know there weren't any plans to make them a kingdom and would've considered them as part of their MittelEuropa plan. Me personally, I don't see them as a kingdom but the same Republic as a German client state ITTL.
On Ukraine: Who rules them? Are they under one of the CP's royal families or are they ruled by the Skoropadskyis? IOTL after the Russians withdrew, Ukraine was briefly a CP-backed dictatorship ruled by Pavlo Skoropadskyi as Hetman of Ukraine before the CP lost WWI and the Ukrainian People's Republic was back in power. Not to sound nitpicky, but this is what IMO would be the most plausible scenario ITTL, though not as a "monarchy" per se.
Are one or more the Baltic states under monarchs or all as republics? There's no formal view on what resulted in the books, but it safe to say for this thread that they're all most likely independent German-backed republics and no United Baltic Duchy was ever created.