Im playing a game against a tec hard ai as the advent and seem to be stuck in a stalemate situation every fleet i send to attack one of their planets gets annihilated despite having more ships .Their star bases are pretty much invincible i send about 10 anti structure ships and they get destroyed long before they can take down a starbase.What tips do you suggest to break this stalemate ?
I looked at the savegame file.
On the economy side of things, I'd recommend scrapping all of your frigate factories that aren't on your front lines and moving them so they're closer to the enemy - then build as many trade ports as you can in the leftover logistics slots.
For military: the enemy has a lot of flak frigates, so you shouldn't have any fighters on your carriers - switch to bombers instead. The enemy also has a good number of fighters on their carriers, so you would be well off building more flak frigates (more than the 4 you currently have) so that your bombers can survive longer.
Note that the asteroid right next to the enemy's homeworld is completely undefended: there's no fleet, nor is there a starbase to make things difficult. If you can attack it and take it over, that'll be a prime spot for then being able to split the enemy even more in preparation for launching another attack. Your plain fleet is much larger than the enemy's at the moment, anyway.
As for fleet composition, I'd recommend building mostly carriers with bombers, a good amount of flak, and a few Guardians (all on Hold Position). Use Repulsion to keep the enemy fleet from engaging your carriers. If you have a decent number of bomber squadrons (75+, hopefully a lot more though) you'll be able to do a ton of damage to the enemy fleet (or starbase) while only being vulnerable to enemy LRM frigates. Adjudicators (starfish) are absolutely horrible at destroying starbases and are rarely worth their cost.
I noticed you also lost a LOT of capital ships so far. If you want to keep your capital ships alive in the late-game, position them on the edge of the gravity well, ready to warp out, and on Hold Position - also use the Guardians with Repulsion to keep the enemy fleet from closing in to engage and you should be fine.
subyugador domina, y otras naves de apoyo...
subyugador domina, and other support ships...
Bad idea. The Domina is probably the worst Advent ship, even worse than the Adjudicator, I think.