SPCR

I need a motherboard that supports multiple AMD cpus, preferably 4 CPUs. Do not use a server-specific motherboard. If you design it yourself, is it possible to achieve it? What level of people can do it? Hope to get your help, thank you very much.

I'm pretty confident that no consumer grade motherboard does this.
As for DIY: Have you made (m)any motherboards before? Takes some pretty advanced tools and knowledge. Getting help from AMD's engineers should also help.

Its likely you will find server grade motherboard with support for dual cpus sockets, but i haven't seen 4, but it probably they exist just not on retail.

I would probably contact server grade manufactures of motherboards like Supermicro and see if they can build custom, they should have the engineers and knowledge for what you want, at least point in the right direction.

I agree. In a regular retail store, such a motherboard will not be. For home use, it is not needed, it will only collect dust. You need to contact the manufacturers of server hardware. They can suggest suitable options.