Your challenge, with a POD of 11 November 1918, is to have Germany keep some of its colonies after a peace treaty with the Entente. Preferably one or more of its African colonies.
This is not doable with those constraints. All of the German colonies had been occupied, sans parts of German East Africa, and that is not realistic for Germny to keep due to British Cape-to-Cairo goals.
Your challenge, with a POD of 11 November 1918, is to have Germany keep some of its colonies after a peace treaty with the Entente. Preferably one or more of its African colonies.
Some time ago I had an idea how the Weimar Republic could get a colony. The POD is that some times before 1914 Germany and the USA signs a neutrality aggrement about Samoa. In the case that one of the signatory get involved in a war, the other partner shall garanty the Neutrality of Samoa as a whole. After the beginning of the war, the USA keep the Allies away from Samoa. But after the Luisitania, the USA demand to send an observing-unit to german Samoa. After that Samoa is de-facto occupyed by the US. This becomes a dejure-occupation after the US DOW. The treaty of Versailles makes Samoa an US-mandat. But the USA don´t ratify Versailles, so Samoa is stuck for some time in a juristical limbo. The US-german peace treaty declares, that Samoa should stay provisorial in US-custody. After Germany joins the League of Nations in 1926, there is a final aggrement. The USA gives the island to the league of Nations and the League gives Germany Samoa as a mandat.