if you expect to work from home all of 2021, submit a new Form ID W-4 to your employer, and write "Exempt" on Line 1. This will stop the Idaho withholding.
https://tax.idaho.gov/forms/EFO00307_12-15-2020.pdf
In order to receive a refund of the incorrectly withheld 2020 ID taxes, you must file a non-resident ID tax return, allocating zero income to Idaho.