Console is great, but for more power, you can directly edit the savefiles.

These are located in Unciv/savefiles/

The savefiles are in a json format (see https://en.wikipedia.org/wiki/JSON)

This is an example of a savefile I made in 4.21.3 with default settings :

• {"version":{"number":4,"createdWith":{"text":"4.21.3","number":1238}}, This contains the version number of the creation of the file.
• "civilizations":[...]}, This contains the list of civilizations (including barbarian and city states) And all of their data. We will expand on this later.
• "difficulty":"Prince","tileMap":{"mapParameters":{"mapSize":{"name":"Medium","radius":20,"width":44,"height":29},"createdWithVersion":"4.21.3 (Build 1238)","seed":1785069853031}, This contains the map parameters when it was made.
• "tileList":[...]}, This contains the list of every tile in the map.
• "gameParameters":{"players":[{"playerType":"Human"},{},{},{}],"espionageEnabled":true,"victoryTypes":["Scientific","Cultural","Domination","Diplomatic","Time"]},"turns":1,"currentPlayer":"Inca","currentTurnStartTime":1785069865125,"gameId":"a3df4dd8-2da2-4168-ac22-2b641cf84451","lastUnitId":20,"historyStartTurn":0} This contains the rest of the savefile, including player type, victory types, turn number, current player, UNIX timestamp of the current turn and other.