Insulating a slanted wall / cavity before or behind insulation

Hello,

I am currently renovating our garden shed (wooden construction), which we recently took over and had to completely gut at first. Now I have a question about insulation, as I have the following fundamental problem:

Unfortunately, the exterior walls are completely crooked – both in terms of the floor plan lines and vertically. For the interior cladding, I now have to build a batten substructure that is straight in itself. This will, however, result in the distances between the interior wall cladding and the exterior wall varying between 8 cm and 22 cm.

My question: Is it better to attach the insulation directly to the exterior wall or directly to the interior wall cladding? In other words, where is it wiser to let the cavity arise due to the greater distance? Most walls and ceilings do not allow insulation thicker than 8 cm. That would mean that, with the uneven crooked wall, up to 14 cm of air would form between the insulation and the interior/exterior wall...
If necessary, here is further information:
The exterior walls are constructed from inside to outside as follows: wooden battens, Styrofoam, roofing felt, tongue and groove sheathing. Inside, I plan to install a vapor barrier over the insulation and then clad the wall with 12 mm multiplex panels.

Thank you for your suggestions and recommendations.

is still just a garden shed and not a second home? If you don't see any risk of moisture in the insulation area, just insulate the entire intermediate space with mineral insulation (glass/stone wool). It is flexible and you avoid cavities (in which something else might happen?)

check whether the slanted wall is not the precursor to the collapse of the arbor, even earlier there were folding rules and spirit levels, and craftsmen/do-it-yourselfers rarely/never built so crookedly. Maybe a tree once fell on it, question to the neighbors

Thank you very much in advance for the answers. The reason the wall is so crooked is that there used to be a raised floor with beams that pushed the exterior wall outward. I have now removed this floor, but unfortunately, I was no longer able to bring the post back. However, it still does not look like it is collapsing, and yes, it is not supposed to be a second home, just nice and reasonably tidy, but if I were to use more than 8cm insulation everywhere, the loss of interior space would be too great. The old insulation that I removed was dry, so I assume there is no moisture problem there. I will probably insulate the entire room as you described. I had feared that if air gaps form there, something might condense - but I have no idea about the subject, hence this question.

Without detailed knowledge of the object, external insulation is always more efficient. Maybe consider blown-in insulation, which is not affected by different cavity thicknesses!? However, I don't know if it is suitable for 22cm.

Thank you HausiKlasi. It is merely a shed, it is not supposed to be highly insulated, therefore blown-in insulation would not be cost-effective for us. External insulation is not possible due to the allotment garden regulations, the outer surface area must not exceed 24 sqm.