There isn't really a black & white yes or no answer to this. It heavily depends on the malware and exploit used to infect the infected computer in the first place.
Ex:
wannacry/etc malware that used eternalblue exploit could infect other computers on the same network, because thats how the eternalblue exploit and wannacry malware was designed (to spread the infection, like a worm).
If its malware that made its way to the PC from an infected download or malware ad that was clicked etc, and the malware is only designed to infect the computer it was executed on but has no worm like properties, then it probably wont spread around. Or if the malware used some exploit to get onto the infected PC, but another PC on the same network is patched against that exploit, then it likely wont spread to the clean PC either since the attack vector is no longer valid on the clean PC (hence the reason why its important to stay updated for software, or like how disabling SMBv1 prevented the wannacry ransomware from infecting other PC's )
Try AP isolation in router setting. It prevent devices from direct connect with other devices on network.
i am not 100% sure about this, since I have not looked into this setting yet, but wouldn't that be counter productive for most home PC's on the same network? And maybe even computers on a company network? Since they would likely want to connect with other devices on the same network to access shared stuff? or access network printers?
Windows has the "homegroup" feature for home users, so would AP isolation break this functionality? Would you still be able to manually share drives or folders if you enable AP isolation? (from your definition of AP isolation, sounds like it would break sharing, but i am not 100% sure).
Not a threadjack, just continuing from the OP's question...
If you have a few home PC's on the same network (wifi or hardwired) and have enabled "home group" feature to be able to share stuff automatically between them, has malware been able to use this as an attack vector to spread to the other PC's? Or is this somehow patched by microsoft?