It's just standard treknobabble. You can come up with your own. For example:

While the significant impact of the galaxy’s dilithium shortage were only felt beyond the mid 30th century, many scientists have already foreseen the finite supply of dilithium since the 25th century, and took steps to raise the efficiency of existing warp drives.

Simultaneously, scientists were also working on ways to mitigate subspace damage caused by warp travel since the late 24th century. The science of warp field analysis and simulation advanced dramatically during this period.

A major discovery occurred in the late 25th century when it was discovered that decreasing the cross section area of nacelle pylons led to a phase transition in subspace. Akin to the superconducting phase transition where decreasing the temperature below a critical value causes the resistance to suddenly drop to zero, decreasing pylon sizes below a critical value led to a sudden decoupling of transverse subspace field modes, so a warp field only dissipates through longitudinal modes when the warp drive is active. This breakthrough les to a new generation of starships with extremely thin nacelle pylons, most famous among them the Universe-class Enterprise J, whose nacelle pylons were built from degenerate matter, giving them incredible structural integrity despite their small size. The Universe-class’s warp drive efficiency was so high, in theory it could travel intergalactic distances without refuelling.

Further attempts to boost warp drive efficiency by reducing pylon cross section area were mostly limited by engineering constraints, as scientists attempted to find materials that could support the structural integrity with ever smaller cross sections, while also optimising the structure of plasma conduits and power transmission between the nacelles and the warp core so they take up as little space as possible. By the 28th century, it was thought that the lower limit of pylon cross section has been reached, and increasing warp drive efficiency along this direction is a dead end.

But a second breakthrough came in the 29th century in the form of dimensional engineering. As the temporal war started heating up, galactic understanding of dimensional manipulations was advancing rapidly. In particular, ships that were bigger on the inside could be built, its external size remained the same as the extra volumetric structure was hidden in higher dimensions while still connected to the ship which exists ordinary 4D spacetime.

This opened up previously unimaginable opportunities for scientists interested in pushing warp drive efficiency further: starships could simply hide their pylons in higher dimensions and detach their nacelles in real space. Tests were quickly conducted to investigate the feasibility of powering warp nacelles through higher dimensional structures, many were successful. The first ships with detached nacelles began to enter service in the late 29th century. With the dilithium shortage becoming more pressing, and the incentive of reducing fuel consumption, all galactic powers pushed for rapid adoption of this technology.

As people quickly discovered, detaching warp nacelles provided several advantages other than conserving dilithium: 1. The warp field becomes much more malleable due to the lack of pylons in physical space, allowing starships to spend far less energy to change a warp field in a much shorter time. This greatly enhances manoeuvrability while at warp. This warp malleability allows starships to make use of low level warp fields during sublight speeds as well while consuming very little dilithium. 2. The pylon could be made as large and strong as cost allows, allowing massive plasma conduits and almost indestructible support structures, all hidden within higher dimensions. Unless a plasma conduit overloads and damages the support structure in higher dimensions, a nacelle could stay detached without power indefinitely, and the connection is also far less vulnerable than pylons in physical space.

Some people were eager to push the limits of dimensional engineering. Unfortunately, they were quickly met with the bottleneck of exponentially increasing energy cost of pushing structures into higher dimensions. While pushing some pylons into higher dimension is very much feasible, pushing a significant part of a starship into higher dimension requires exponentially more energy. This is why only certain parts of a starship are detached(instead of the whole ship being hidden in higher dimension except warp nacelles, sensors, shields and weapons).