Network Neighborhood on Windows 11 is just slow by nature. The mobile app feels fast because it doesn’t use SMB browsing. Make sure SMB2/3 is enabled on the NAS, SMB1 is disabled on Windows, and that your PC/NAS/Switch all use the same MTU (usually 1500). Easiest test: skip Network Neighborhood and open it directly with \\DS925 or the NAS IP. If that is still slow, then it’s a network config issue, not Synology