Yes. A Will can be contested if the execution of the Will was not properly witnessed.
The reason that the witnesses are required to sign your Will is for caution sake. It is to prevent any doubt that could arise from the Will actually belonging to you as the witnesses can be there to attest to it.
A Will not witnessed is a Will that is not recognized by law despite having your signature on it.
Koha places an importance for you to select your witnesses to your Will. Therefore, under the “Witnesses” section, you can designate up to 2 individuals to validate and confirm your Will validity.