Hello, first try to see if the issue is with your network or SMB. iPerf3 can tell you that. you will have to install iPerfs on your NAS , run it in server mode ( with docker support it is easy you can look for tutorials). then check the speed betweeen your mac and nas with iperf client.
If iPerf shows good speed - then the problem with SMB settings
But I think you will find that iPerf is slow too , which would be a wifi bottleneck