Dad tired of living. Any suggestions?

I'm sorry for the stress this must bring you. I hope you have had some conversations about EOL end of life, if not start talking about it. At some point the will to live ends, don't let it be a surprise. We all are only here for so long and then we pass on. At some point you have to let your loved one go if that's what they want and be at peace with their decision as hard as it may be.

do the best you can, make his life happy, do not argue with him, tell him you understand.
As alvadear said, truth... make it about the truth.. tell him, you understand, play music, give him his favorite treats and the caretakers... it is okay.
give him his party with all the hoopla.... it is okay..
these bodies are not made to last for ever... so.... if you find something he enjoys... let him enjoy it... food, treats, music? movies etc... bring em on!

My Dad was the same. He was exhausted with life and I would lay on the bed beside him and let him tell me about it. I was a nurse and had so many patients tell me that, and tell me they could not speak with their families about it. My Dad wanted to tell me he had a wonderful life, a good life, wanted to tell me about the one thing he had done he was sad about, wanted to tell me he just longed to sleep, and it was so hard just to get up "for your Mom" and just to eat "for your Mom" and to get on scale "because she makes me" and etc. After he was gone my Mom said she was sorry she had pushed him to stay with her; I was able to tell her he always knew it was out of love.
So my advice, let him tell you. Tell him you understand he is exhausted. That you aren't ready to lose him, but that you will love, remember, pass on anything you learned.
Your Dad is ready. Please, and with all my heart, acknowledge that. It is hard to understand, but you will get there, and now, pushing 79, I understand how close it is. We get tired. We are ready. Please be happy about that for us. And I must tell you, my Dad will never be gone from me, nor yours from you, but what a grown up gift you will give him by sitting and saying TRUTH to him now, and listening to his own truth.

My dad didn’t have dementia but he definitely reached a point of wanting this life to end. He did take Zoloft his last few years and it was a help with being depressed. But it’s very understandable for a person with multiple medical issues going on, missing those who’ve gone before them, and not seeing a bright future, to want out. Mostly I just told my dad that I understood

My Dad was ready to go for a couple years before he passed. We would talk about it & sometimes I would tell him I wasn't ready to be without him. He had a DNR & did not want any extra measures taken to sustain him, which I strictly adhered to. The day I got the call that he was fading, I gathered what I needed because I would be beside him til the end. He would rouse and talk but eventually fell unresponsive tho I could still see recognition in his face. I talked to him for several days before he passed, sharing memories & stories he'd told us growing up. The day before he passed, the aide brought him breakfast but he wasn't interested until I mentioned his fave cereal was included. He roused, ate the entire bowl, drank some coffee, spoke to me then laid his head back on his pillow and was back to being unresponsive. It was wonderful and heart-breaking at the same time. He passed early the next morning & I was at peace because I knew he was where he wanted to be. In heaven with my Mom, his Mom & his Father he hadn't seen in 84 years.

I watched this play out with a gent at my mom's nursing home. While on the one hand he seemed physically and mentally much more capable that most of the people there on the other it was undeniable that he had a low quality of life and his future was only likely to be something worse. I made a vow to myself that I would never force my mother to eat - wheedle, plead and tempt maybe, but never, ever force. The very old have so little control over where they go, what they do and even of their own bodies, the choice to eat (or not) is often all they have left of their autonomy. Yes do look into whether antidepressants help, but also be willing to allow him to make his own choices about this.

Depression in seniors is very often overlooked. May want to talk to the doctor and see if he has it and can be treated.

I don't know if you have done it already; but getting him occupational therapy and/or rehabilitation care could be helpful. If he is starving himself he would end up on IV nutrients and possibly anti-depressants by IV as well until he gets better/until the end. Hard to get enough vitamin D for the elderly especially during COVID let alone winter, which makes things worse. Also I always heard trying to play music and/or tv shows etc from their prime could help reactivate happy memories.