Is it possible to simulate a glue-like fluid to stick flat mesh wall? I've tried different settings to make it thicker and slower but it always slides down like wet cement. What should I try that doesn't put too much pressure on even the most beefy computers?
It is not possible to do this in mantaflow, no. The simulation lacks any setting on effectors that would make such an interaction possible.
The problem is that the stickiness bit is actually a chemical interaction that a fluid simulation doesn't model.
It's probably possible to fake it, depending on what you want the effect for. You can have the simulation generate a mesh, setting the Viscosity and Diffusion in the Domain object as you have been doing and the density of the liquid in the Flow object. After the bake, pick the frame that has the result closest to what you want and use it.
You can also mess with the Field Weights in the Domain object, but I've never found that to be satisfactory. Of course, when you do that, you also reduce the realism of the simulation. At that point you may as well just use a procedural material on the surface objects to 'apply' the liquid.