You have lots of choices and all of them relate to risk of collapse. And there are different kinds of collapse.
There's the basic big section of a wall slumping down behind a liner. Sometimes severe enough to lower the top allowing water out and behind the liner and making the problem even worst. Sometimes just a bulge.
Another type is sharp soil edges eroding over time. The rock in Fig B can end up sliding into the bottom of the pond.
The simplest risk reducer is a single block color with the blocks filled with soil. The walls are sloped, kind of pre-eroded. For less risk bond beam blocks can be used with horizontal rebar and filled with concrete. Another option is to pour the collar using rebar and forms and no blocks. Bond beam blocks basically act as forms so they're less work. Also cheaper for DIY builders. Pros can reuse forms over and over so their cost is cheaper for them.
Another option is no collar or retaining wall behind the liner. Collapse risk is highest with A, but still better than just soil and liner. By sloping the wall in B the soil is less likely to collapse and you end up with a collar on the inside of the liner. Because of the center of gravity the mortared rock has it wants to fall back, against the soil. So although the end result is visually a vertical wall there's little chance of it falling over into the pond like A might. In C the blue is some reinforcement mesh and the mortar is extended over the liner top and down into the soil. That can provide a little more strength, but probably not needed.
Notice in all cases the vertical rocks rest on top of a foundation rock, or concrete can be used.
Also the rock doesn't have to be vertical, it could just be mortared against the liner so it was sloped like the liner is. The center of gravity is still the same, pushing against the liner. Purely whether you want a vertical or sloped look.
Here's a block retaining wall with a mortared rock veneer over the liner. There is still a soil shelf with a sharp edge that will probably erode over time but there's no rocks or plants on the shelf to end up at the pond's bottom. The shelf is wide enough that hopefully the erosion is never bad enough to under cut the blocks.
This shows the rocks mortared long wise, like tile on a wall. The rock could also lay flat and be stacked. Just depends on the look you want. Notice there is concrete at the base of the rock as a foundation.
A full retaining wall system can be used to virtually eliminate collapse risk, but of course at a higher cost. The red is reinforcement mesh.