My spouse, who has many medical problems plus dementia, chews his oxygen lead to nose and breaks them. Ideas on how to get him to stop?

Can you place the tubes behind his head? Rather than going down in front bring the tubes over the head so they are behind him.
My Husband was a chewer. Clothing, towels, cloth napkins, his hand. fingers. I looked for soft baby chew toys and got a few of those. It worked and he grew fond of a little bunny that he would chew the ears of.
Some of the baby chew toys and other finger toys crinkle and make sounds, most are soft and they are pretty durable. The other toys that worked well for me were soft dog toys. Again some are soft, meant to be chewed and durable.

Hospice oxygen is often for comfort and if your spouse is chewing and presumably removing the tubing, it is doubtful if he really needs it. Unless he has some kind of observable and medical need for it, I doubt he really needs it since he is already not using it.

The danger of this is he may chew off the nose part and swallow it.

Restraints are not an option--and taping the tubing down is more likely to be more irritating. So what else is there? Leave it off and let him be. Note Sedation will decrease his respiratory drive--he may be knocked out, but it can also kill him. I mean sedatives will decrease his inspiration/respiration drive so oxygen therapy is a moot point (unless he's intubated on the hospital's unit and full code).

PS: Do ****NOT**** try the aluminum foil suggestion. He will chew and swallow the foil and it is a very serious choking hazard. People with Alzheimer's do not sense the unpleasantness. Also do NOT use lemon juice on the tubing or other noxious food because that can lead to mouth sores and impair what little appetite and ability to swallow thickened water he has left, which creating mouth sores hinges on being cruel.

Mesh cord covering, got mine on Amazon. Expandable, chew proof and not dangerous in mouth. Or paper towel/ tp rolls slit to go over that part-?
The cat would chase my mom's oxygen tubing, and bit holes in it at the most inconvenient times! I had to find something. Cord covering worked very well.

You might try covering the hose with aluminum foil and give him an old hose that he's already bites to have to bite on

Since he is on hospice, I would recommend removing oxygen tubes and maybe use an oxygen tent at night.

my grandmother on hospice can you give him maybe ativan to calm him?

Imho, there are many O2 lead coverings for sale to prevent chewing.

Would it be too cruel to coat the tubes with lemon juice?

Are we talking about a nasal cannula that goes across his cheekbones and loops over his ears, running under the jaw and meeting under his chin? And he's taking it off and chewing through it?

Search out a bitter/spicy liquid to coat the tubing like parents use to stop nail biting.