If you just want to load a single layer, this code should work fine:
class MyModel(nn.Module):
    def __init__(self):
        super(MyModel, self).__init__()
        self.fc1 = nn.Linear(10, 10)
        self.fc2 = nn.Linear(20, 20)
        self.act = nn.ReLU()
        
    def forward(self, x):
        x = self.act(self.fc1(x))
        x = self.fc2(x)
        return x

model = MyModel()
torch.save(model.state_dict(), 'tmp.pth')

state_dict = torch.load('tmp.pth')
model = MyModel()
with torch.no_grad():
    model.fc1.weight.copy_(state_dict['fc1.weight'])
    model.fc1.bias.copy_(state_dict['fc1.bias'])