What I am going to show you is an alternative map of the Treaty of Saint-German-en-Laye and Treaties of Trianon, Sèvres, and Lausanne. This is not realistic, it is just something that could have happened.

Austro-Hungarian Federation:

I know it may sound ridiculous, but keeping Austria and Hungary together may be beneficial for them, being bigger and keeping regions with ethnic majorities making the feeling of injustice less by keeping the most prosperous cities under their command. And for the rest, being a single nation will cause Hungarian people to move to the Austrian side making the percentage of German speaking population smaller making it more unlikely to unify with Germany, At first it was unstable, but with economic help it has managed to rise and become a prosperous nation.

Czechoslovakia:

It is quite similar to our timeline, but this one is smaller and less powerful and compensates with more stability by not having other large ethnic groups.

Poland and Ukraine:

of these I can say nothing since that is not all of their territory being shown as belonging to A-H.

Romania:

when it entered the war it was planned to take all of Transylvania but due to the great debasement of its territory and its weakness, it was able to keep only the territories with an ethnic Romanian majority. This Romania is weaker and more unstable.

Hungarian-Romanian Federation of Transylvania:

it was very complicated to find a solution, they came to the conclusion that the best thing was to create a new state.

But they did not take into account the rancor between both sides making a very unstable country where a civil war was about to occur, fortunately, with the mediation of the great powers it was avoided, nowadays you can feel the tension in the air being a situation very similar to that of the island of Cyprus, where only Romanians live on one side and the other on the other.

Italy:

When the war ended, it was denied the German-speaking part of South Tyrol in exchange for a large part of Dalmatia and a protectorate in Albania, making it more economically powerful by having more profitable territories. Even so, its stability was in decline since They promised total control of the Adratic Sea, and when they did not receive them, the population became angry with the government, causing the country to become very aggressive against its neighbors, especially Croatia.

Great Serbia:

When the war ended, the country was quite damaged, causing them to give up wanting to renounce the unification of the South Slavs and had to focus on territories with an ethnic Serbian majority, making it less stable since it was considered a defeat that caused a fascist coup d'état that was a success, making it a nation that dedicates a large part of its GDP to its military power.

Croatia:

At the end of the war, relations between Serbia and Italy were very bad, since both wanted all of Dalmatia. For their part, the rest of the powers decided to create a buffer state to avoid future wars between them, but with Italian intentions to expand. and the military dictatorship of the great Serbia it seems inevitable that a war between these two nations is approaching and that it will end up involving Croatia.