I had a relative with a similar situation, before 2018 (when W-2 employees got a deduction). I advised him that he needed to split the deduction, based on time spent on each job, between Schedules A & C.
I'm of the opinion (but cannot cite a reference) that if you meet the convenience of the employer test, for the W-2 work, you may still deduct the time adjusted portion on Schedule C (self employment) since the home office was used exclusively for work (W-2 and self employment). However, if you don't meet the convenience of the employer test, then the home office was not used exclusively for "work" and you get no deduction foe even the self employment use.
