Hello @tonjunee ,
I believe you may be getting some terms confused. You do not depreciate inventory; rather you do a physical count once a year, and enter an inventory adjustment for the variance between what was on your books and what you actually have in your possession. The differences could represent a lot of different things, depending on the type of business; theft, old or obsolete and unsellable, give aways (in which case you would use Advertising as your write-down account), etc. or any other reason which you are aware that has affected your physical inventory numbers. This inventory adjustment to actual can be put in an ordinary expense account or COGS, whatever works best for your business.
However, your fixed assets are depreciating each year. CRA has determined what types of assets go into what classes, and each class has a pre-determined rate of depreciation per year. For tax purposes, CRA calls it CCA (Capital Cost Allowance). The accounting entry for this is to Debit a Depreciation Expense account, and CR the fixed asset account by the rate of CCA allowed in the year, thus reducing it's book balance. If you sell a fixed asset, any cash you receive for it that exceeds the book value, is posted to a Gain on Sale of Fixed Assets other income account, or if you receive less cash than the book value of the asset, the difference is posted to Loss on Sale of Fixed Assets expense account. Some people combine the two into one account and call it Gain/Loss on Sale of Fixed Assets, using income or expense account, depending on which one is most favourable looking to you on the P & L.
Many people leave these entries to their external accountants as they can be a bit tricky if you are not familiar with all the rules. Most depreciating assets are also subject to the half-year rule, meaning that in the year of acquisition and the year of disposition, you are only entitled to depreciate 50% of what you would normally depreciate. So if the depreciation rate for a particular type of asset is 30%, you would only be able to depreciate 15% in the year of acquisition or disposition.
Here is a link from CRA that may help you: https://www.canada.ca/en/revenue-agency/services/tax/businesses/topics/sole-proprietorships-partners...
Hope this helps somewhat. Good luck!