If I may correct a few errors above, to avoid possible confusion.
All SMB devices broadcasting any Bonjour / mDNS parameter will be automatically displayed under 'Network' - the networked device does not even have to be a file server, or previously connected to, to appear here. No utilities or apps needed. In the screenshot below the Window's PC icon is actually a Bonjour capable HP printer, but as it is broadcasting a Bonjour flag (printer and scanner in this case) it will be shown here. The only exception to this is the local device, my MBP in this case, which is not shown under 'Network' but is shown in the 'Locations' sidebar:
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If you select a file server (eg the first server shown in the list - 'Dragon' a Synology RackStation) that you have not connected to previously you will be asked for your credentials. Some light icon humour here: Apple-friendly file servers are shown as the old Apple xServe, PCs/Windows are shown as an old and yellowing CRT display with the blue-screen-of-death and Apple devices are shown with their respective icons.
Once you have done so the handy connection icon should automatically appear in the left sidebar whenever it is broadcasting the Bonjour SMB flag [_smb._tcp.]:
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If you select this server from 'Locations' (with the normal / default SMB settings) it should connect using your previously stored credentials:
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...and display the SMB file structure you have made available on the Synology NAS (in this case I only have 2 folders visible to this user):
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All of the above is being done without the Server / NAS / whatever being actually mounted (ie no 'eject' caret being displayed on the sidebar). Once the credentials are completed for the first time all of it is automatic, no dragging of anything or trying to find a server that isn't on the Locations list. It is either under 'Network' alone (when not previously accessed) or in the Locations sidebar. As servers or Macs become available / not available they will appear or disappear automatically from the sidebar.
If you access a top level network share folder (Spare Shared Folder 1 in this case) then macOS will automatically 'mount' this folder and display the eject / un-mount caret:
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Some macOS applications will mount and unmount network shares as needed. Other may presume that the share is always mounted and may fail when they try to access a folder.
There are some simple ways to always mount a given location - I use the Users and Groups>Login Items to always mount a volume used (eg for Plex recordings). To avoid a situation where a network share has been accidentally unmounted I use an app called AutoMounter that, as the name suggests, automatically mounts a network share should it fail for whatever reason.
Of course, for regular human use you just click on the sidebar icon and everything to mount a drive is done for you - mapping, assigning drive letters by individual users is the incredibly dumb way Windows manages network shares. This is macOS, where things are simple.
Don't forget that macOS Finder and Synology Universal Search can cooperate (no such luck on Windows), so a Finder search can reveal a file on the NAS by its contents or indeed by any other granular method provided by Finder.
(I have deliberately avoided any reference to the depreciated AFP format because... it is depreciated.)