Biology - glycolysis

I don't understand why the link reaction and krebs cycle cannot occur without oxygen because glycolysis use nad+??

Both NADH and FADH2 transfer electrons to complex I (NADH) and complex II (FADH2), these are protein complexes in the cristae of mitochondria.
The electrons are carried on an electron transport chain, being reduced and oxidised, lowering their potential energy. This energy is used to actively transport protons (H+) from the mitochondrial matrix to the inter-membrane (space between cristae and outer membrane of mitochondria) space. Protons facilitated diffuse through hydrophilic channel attached with ATP synthase. The kinetic energy from the proton rotate the motor (that binds to ADP and Pi).

The final electron acceptor, at the end of the electron transport chain, is oxygen. This will accept protons and electrons to form water. Without oxygen, the electron transport chain would stop (as the electrons would eventually be unable to be transferred between proteins in the electron transport chain). FADH2 and NADH wont release electrons.

NADH and FADH2 unable to accept electrons in the citrate cycle (krebs cycle), so that cycle would stop. The links reaction uses NAD+ to accept electron to NADH, so it is also stopped.

This is the reasoning behind anaerobic respiration - an electron acceptor being used after glycolysis as glycolysis produces net of 2 ATP through substrate level phosphorylation. In particular, NAD+ accepts electron when triose bisphosphate breaks down to pyruvate, releasing 2 phosphates that form 2 ATP (glucose produces 2 triose bisphosphates). For respiration to continue, an electron acceptor is required so NADH can release the proton and electron to form NAD+

In animals, pyruvate acts as the electron acceptor, forming lactic acid.
In plants/ yeast, it is called fermentation. Pyruvate forms ethanal by pyruvate decarboxylase, releasing CO2. Ethanal acts as an electron acceptor, forming ethanol.

so for anaerobic respiration - I understand what you mean when you say how Fadh and Nadh cannot be oxidised because oxygen is the final electron acceptor so oxidative phosphorylation, krebs cycle and the link reaction stops. BUT specifically in glycolysis where does the nad come from which oxidises triose phosphate? - I understand that the NADH is oxidised releasing electrons which are accepted by pyruvate to form lactate or ethanol etc. but where does that first nad come from lmao in the most simplest terms?