The flat-rate method for employees who worked from home is not available for 2023. You did not need to get a form from your employer.
If you worked from home in 2023 and who are eligible to claim home office expenses will have only one option — the “detailed” method, which will require a completed Form T2200: Declaration of Conditions of Employment from their employer. The CRA will release the updated T2200 form and guidance in late January. Visit CRA then for more details. https://www.canada.ca/en/revenue-agency/services/forms-publications/forms.html
If you are the employer, start putting procedures and policies in place now, and letting employees know about when they might receive T2200s in order to manage expectations and reduce confusion.