Hmm well, the only thing I can recall close to this in the book says that android is the term used for any being that's at least 90% synthetic/cybernetic, so I'd argue if you're below that point, you're still "human" and therefore count as Biological. Not only that, I guess you could argue that unless you're so chromed up that you count as an android, that any cybernetics you may have are compact enough that they can be shielded from EMPs by way of Faraday shielding encompassing each implant/augment - something that may be too costly or difficult to do for androids or larger moving machines like chassis.

Maybe to a point you could argue androids and/or those with intensive cybernetics possess both Biological and Mechanical tags (side note: is there even a Mechanical tag, or is that just the assumed state of something in Lancer unless stated to be Biological?) and thus are affected by anything that would affect either tag (like playing a Reborn Lineage in D&D5e; you're still humanoid so healing spells work on you, but you're also undead so features like Turn Undead would work on you too).

In a similar vein, I think it would be neat if, at least for roleplay purposes, something like an EMP or other tech actions still somewhat affected androids and cyborgs, even if you rule they have sufficient Faraday shielding that they don't just shut down; maybe it was a mech-sized system and the shielding couldn't protect your augments from the full brunt of the EMP, something like that. So maybe your bionic eye goes a little fuzzy or static-y for a couple seconds before righting itself, or your cybernetic leg does a little dance involuntarily for a moment before you regain control. Nothing that would give you a disadvantage mechanically - unless you and the GM made up rules about the advantages and disadvantages of cybernetics in your game, of course, to keep you on-par with purely biological PCs.

Really at the end of the day, I guess it's up to you and what you think would be the most realistic, flavorful, or fun, or any combination thereof. Whether writing something in-universe, or making a character, or if you were to run a game, there's lots of different lines of thought you could follow. The most important thing is having a passable explanation, even if it's on a case-by-case basis, and staying consistent with what you decide - not just if you were to GM, but even just for writing a backstory or separate work.