How many layers of spunbond NWPP?

I have sheets I bought from Amazon. They are specified at 38 gsm, but I measured them at 43 gsm.  You may just have shopping bags - because your city banned plastic bags.

Keep folding the material you have and see if it fits under the presser foot:

(fold fold fold fold ... to work out what your sewing machine's limits are)

If you had an 8 layer Rag Mask Max, sewing the central seam half way through making the mask is 16 layers.  It is always double. If your presser foot can handle 24 layers of your material, then the most layers of mask you can sew is 12 (half). That's your guide.