There is Defence in depth, which means giving up territory for strategic gains and to keep your units intact. It also enables you to create situation that are favorable for you to attack and stretches enemy supply lines.

In terms of the Southern attack into the direction of Crimea defense in depth can't be used too well as the supply line is either north of the sea and thus on land, which is good, or over the bridge and all the way over Crimea which is bad.

So the extreme points are holding completely (which means focusing your troops on that area, which means that other areas are more easy to be contested), or withdrawing after tactical fights to lure the enemy into your formerly held territory. A mixture will happen. When Ukraine is able to push further into the territory a natural response would be to try to create pincer movements with reinforcements to make the forward troops encircled and force withdrawal.

Since all this happens in areas of mine fields (at the front) and artillery barrages both sides are currently focusing plenty forces which is dependent on supply chains. This doesn't mean it is a trench or positional warfare, but only has some elements of it within that area.