And it's not even a tax write-off until you have enough income to offset expenses. (Which is nice as far as it goes but is small scale where you can write-off a few $K in expenses against a few $K in income.)
If there's already income paying the pesky mortgage, you start up an official business as a side hustle. As long as you are showing income even if at a loss, you then get to use that loss as a deduction. If it never pans out to be profitable to the point the tax man strongly suggests the business should close, you close it. In the mean time, you've followed a passion, that even as a loss, still gives financial benefit helping with the pesky mortgage.
There's doubtless some wiggle room but it's like home office deductions. Triggering an audit by the "tax man" is rarely a good idea for most people and may well cause accounting bills that exceed any marginal gains.
If there's already income paying the pesky mortgage, you start up an official business as a side hustle. As long as you are showing income even if at a loss, you then get to use that loss as a deduction. If it never pans out to be profitable to the point the tax man strongly suggests the business should close, you close it. In the mean time, you've followed a passion, that even as a loss, still gives financial benefit helping with the pesky mortgage.