I think this varies between jurisdictions. I believe it is deductible in the USA, but not here in the People's Republic of Kanuckistan, although there are ways around the limitation, depending on your appetite for the risk of a drawn-out battle with the Canada Revenue Agency.

Up here, home mortgage interest is only deductible if the home is used to generate income, so it does not apply to people who use a home as their primary residence. But what if you have a home office? What if you use it as an AirBnB some of the time?

If you ask a tax accountant whether Canadian home mortage interest is deductible, they will answer "a definite maybe." But it's actually "no" for most people who don't structure their home ownership around qualifying for a deduction.

That second part is huge and people don't account for it correctly. It really hasn't mattered much in the era of super-low loan rates, but the amount that your mortgage is deductible is only the difference between the standard deduction and the itemized deduction.

My mortgage interest became "worthless" for that when the standard deduction was raised. I'm still better off than before, but that particular part of the benefit is gone.

The standard deduction for California did not change, unlike the temporary change on the federal side enacted for 8 years beginning with 2018. Also CA did not change the limits on the amount and type of loan interest that is deductible.

Since California by many measures is large enough to equate to a "country", It would be fair to add it to the list of places where primary residence (and a second home too) mortgage interest is largely deductible.