Victories in my opinion are pretty monotonous and boring. This is probably because of the lack of competition and diversity. I think there should be different possibilities for each victory type and is randomised in each age when you start the game. Here are some potential options for the modern age:
Cultural Victory:
Bring back great people and great works. This is honestly one of the biggest things I miss from civ 6: all the pieces of great art, music and sculptures were nice to look and learn about. In general even the relics and codicies from previous ages seem pretty generic and would benefit from great people. This would solve the problem of lack of competition as now people will be trying to convince the great people to join their civilisation. You could make people join your civ by creating relevant buildings for example:
Great Writer: Build libraries to attract great writer xp
Great Musician: Build opera houses to attract great musician xp
Great Artist: Build studios to attract great artist xp.
Make it so that a city can only have one of the three buildings so you have to commit to one type of great person per city and actually have a challenge in this victory type. As a bonus these great works would actually make sense in this age (1800s-1900s)
Military Victory:
Generally this is pretty easy if you have good science and strategy. If not all you need to do is not cap any cities for the first 2 ages and then go nuts and cap all the islands in the modern age. So I propose that instead you need to have a certain amount of capture points in order to win the game victory (similar to hoi 4). So for example you need 100 capture points:
Enemy capitals can be worth 30 points
Cities over 40 pop can be 20
Cities under 40 pop can be 5.
Or you can just bring back cap all capitals goal- thats good too. Obv adapt this based on how many players there is etc
Economic Victory:
I think this is probably the most generic and boring victory I have ever seen. You can win this by literally holding shift and spamming enter once you've placed resources into your factories. I dont see why for example having 10 cotton resources should make me win the game... It is a raw material. I propose that once you have unlocked a certain technology you unlock a factory and get given a range of things you can manufacture. To win you need to craft 10 different items all which have their own recipe and amounts of production.
This would mean that to make a carriage for example you will need 20 horses, 15 hardwood and 30 rubber. (i will explain in a second) These items should be the same for everyone and allow for civs to restrict trade of specific resources that they need. For this reason I think you need to bring back the Civ 6 Gathering Storm (?) system for resources where every turn you accrue a certain amount of each resource depending on how many copies you have. You should also be able to restrict which ever resource you need from trade.
Similar to cultural victory this will help with learning history and the different rare and expensive items that existed.
Science Victory:
This is a pretty staple victory and realistically could stay the same but here is an alternative. If you played really well in the exploration age in terms of science you generally can just steam roll this victory, and similarly to economic you can just click on the last tech and shift enter till the end of the game. I kinda really like the idea of making items based on recipes so this victory can follow a similar pattern. Instead of building rare and expensive items like in my proposed economic victory you can be building different parts of the space ship.
Since this would be a science victory make the item requirement less and focus more on science needed to unlock.