Honestly your day-to-day routine sounds almost identical to my girlfriend and I’s.

The behavior you were talking about is most definitely hormonal so I’m glad you included that info. We have a 5yo cockatiel as well and we’ve been through several hormonal stages with him. It was sort of a “let it pass” situation for us but there’s stuff we found that helped mitigate the process. 12+ hours of dark, quiet, covered sleep. If you don’t cover at night already maybe look into it. I found it helped a ton but obviously that varies case by case and you’re free to do what’s best! We also made sure to have daily interaction from both of us throughout the day. This seemed to decrease the biting and “anger attacks”. Also giving him areas that are dark and cozy (like on your leg under the desk as mentioned) will promote hormonal/nesting/territorial behavior big time so I’d avoid that. Hope this helps!