I’m not sure anything i say would be helpful to you as my experience is from a female view, but tamoxifen really messed with my interest in engaging in life and I did a lot of sitting around when I was on a higher dose of tam (20 mg). Changing to 10 mg didn't help, but I’m fine on daily 5 mg. Of course, you need to consider what the best dose is for you to reduce the chance of recurrence.

Id suggest an antidepressant but some of those reduce sexual drive.

I looked up anhedonia, and this was suggested: “Targeting Dopamine/Norepinephrine: Drugs like bupropion, vortioxetine, or ketamine may be used, as traditional SSRIs (serotonin-focused) can sometimes worsen emotional blunting.”

Personally, I’d try ketamine if I were you. You’d have to be careful on dosage. There is no antidote for an overdose. But I've read good things about it. I hope you find an answer and can move forward with a happy life!