I have never seen Gardening Leave used in this manner.

Usually (and I know this from personal experience) if you are senior enough you have a notice period of 3-6 months and under normal circumstances you are expected to do a proper handover before leaving. Sometimes they don't want you to come in to the office or have access to the corporate network/data but they still want access to you in case they need it.

Non-competes are usually 18-24 months and I don't think anyone is going to pay that for you to sit on your butt.