1. "UI Size" - The UI needs scaling, can increase it with + or decrease it with -. 100%, 110%, 120%, 130% etc. to 400%. 100% is usually 1080, 150% for 1440, 200% for 4k. Do no need to restart game to apply changes. Maybe drag to the resize UI? This would be a godsend.
2. Fleet manager - New icon in lower left part of screen "Fleet Manager" shows all ships currently part of fleet and their stats. " - " and " + " icon to decrease or increase the number of ships along with a "Remove Ships" from fleet and "Retrofit" buttons. Ships will now retrofit while inside a fleet but unable to move. A list to show current ships being built into the fleet showing number of turns till completion and before joining the fleet. Right click to cancel construction of ship with an available "Rush" production of ship icon on list. If you increase the number of ships in the fleet, nearby shipyards will start building the ships, joining the fleets automatically once completed. An alternate way is to have ships be invisible once completed in the shipyard. After X amount of turns the ships automatically appear in the fleet.
3. When building a starbase the game automatically renames the starbase. Example: Building a mining starbase, the starbase will automatically get rename to "Earth Mining Starbase". I have to rename all my new starbases.
4. Cultural Progression - If an ideology spawns a ship, the ship's icon appears near it. If you mouse over the ship icon it will show the stats of the ship. If an ideology unlocks an improvement, the improvement's icon appears near it, mouse over improvement to see the stats. Lets not forget ideologies which unlocks tech. This annoyed the heck out of me since GC3.
5. Manual placement of Shipyards after completion- Sometimes planets randomly places the shipyard in the south but I want it in the north. Sometimes objects such as asteroids get in the way, that's why I want it in north. Maybe a "Relocate Shipyard" button. In GC3 you can build a shipyard with a constructor but not in GC4.
6. Save games from the same race are in same folder. Select load game and pick which race's save files you want to load. Less clutter in the save files.
7. Expand the UI to display additional resources. A new expanded row below to display additional resources. It's a hassle each time having to click the > to check your resources.

8. The fleet UI has difficulty displaying more ships if fleets get too big, or the ship icons get too small.
A. Move ship icons a bit to the top right giving it more room.
B. Move the middle bottom UI to the right, but it's going to create the same problem if fleet is fill with many smaller ships.

9. The tech tree UI and design is atrocious and outdated design from GC2. I made multiple posts about it from 2015 and beyond.
https://forums.galciv4.com/467356/page/4/#3611171
Look for "A better tech tree interface/UI"
10. Below screenshot is in 2560 X 1440 resolution and UI size on medium.

11. Race specific techs or techs granted with traits/abilities should have an special icon in the tech tree.
12. Need a "Kill citizen" or "Exile Citizen" button. Temporary approval penalty if citizens are same race as your main race. Evil races such as the Drengin gets an approval bonus. Exile Citizens will seek refugee in other factions.
13. If a core world culture flips it automatically removes the enemy's shipyard.
14. Enemy starbases can culture flip, if a starbase culture flips it is destroy automatically.
15. Confirmation before "Destroy Improvement" in the planet screen.
16. In the "Factions" screen, left clicking on a leader menu doesn't appear to fire, gift, or execute them. The menu appears in Ministers, Governors, Diplomats, and Commanders.
17. The cursor when you're trying to type, makes it hard to see what letter is there. You might have a space in the exact spot but can't see it.

18. Ability to select which side to eject ships from shipyards, planets starbases etc. This was possible in GC2 or GC3.
19. The rally points on the map aren't noticeable enough. It needs to glow more and use a different color. At the top right of screen under "Ships" it now shows rally points or make a new Icon.
20. Top right of screen under "Ships" if you left click the down or up arrow icon the menu goes to the top automatically. Annoying to say the least.

21. Transparency setting for menus.