Don’t bother with M-discs. They only provided a meaningful advantage in the DVD era. I’ve researched this a bit myself and consensus at least in the data hoarding community is use 2 Blu-ray Discs from two different batches (bought 6 months apart). Which still comes out cheaper or the same as branded M-Discs. (Though that may be overkill and truth be told as long as you test the disc and it’s data done months after writing you’ll tend to catch any rare bad ones)
Truth is, quality Blu-ray Discs have all the features that would engender M-disc type longevity in the design spec. Just make sure they’re not low to high (LTH) discs which are inferior but always marked as such at least.
Don’t get no-name cheap ones either, get Verbatim, Sony, some other good Japanese brand. For Verbatim specifically their discs marked MABL on the package are better.
Always burn data at lower speeds too, less errors.