“Congratulations! You’ve reached the right person! It’s [your name]. Unfortunately, you’ve called at the wrong time. Please leave a message with all your contact information, and I’ll call you back within 24 hours.”
In practice, most businesses are simply handling this on a case-by-case basis since COVID is a temporary problem. Most home networks can handle the extra load as long as the employee makes sure that other latency-sensitive traffic, like gaming or video streaming, is kept to a minimum during the hours when they need to talk. If some home routers develop problems, IT staff simply build a queue and handle those one at a time. Sometimes they'll be able to access the router remotely with the employee's permission, sometimes they'll have to walk that employee through configuration steps to fix the problem. Sometimes the employee will just have to live with it unless the company springs for a new router or a higher bandwidth tier from the employee's ISP.

23. Howdy, thank you for calling [business name]. Please toddle away your title, quantity, and a short message, and a member of our team will return your name within 24 hours.
4. “Thanks for calling [your company]. We’re looking forward to speaking with you. Let us call you back as soon as we are available by leaving your name, contact information and the reason for your call. Have a great day.” A simple, concise, and, of course, friendly voicemail greeting for your main business line.