I am currently using a synology DS420+ for all backup but more for long-term storage scheduled daily at night. From. Currently using it for daily backup.

My current setup is everything from my mobile/work gets backed up to Onedrive and then at night gets mirrored to the NAS. My workplace has downgraded my OD business from 1 TB to 10 GB. As such, now having to change setup to backup all to NAS and Onedrive to direct sync to the NAS. My Unifi is 300mb if I am not mistaken. Is there a way to maximise the upload/download speed to the NAS? The NAS is connected via wire to a TP link AX10 router. I want to saturate the bandwidth for syncing purposes. I also have 2 other work colleagues sharing my NAS for their work. Though the their usage is minimal (around 200 gb and 4 gb for each user). I have 3.7 TB stuff on there and my OD alone accounts for 500+ GB.

I did not bother to install the SSD in the NAS as the unifi speed ain't going to support it anyway. To things in context, the AX10 router is connected via wired to CCTV, NAS and wireless to CCTV, smart home (IoT devices-vacum, filter, smoke alarm, smart switch, alarm), and total 30+ devices (tablet, phone. laptop, tv etc). I don't see the need to upgrade the bandwidth as even with 3 people having online meetings, few devices on youtube/netflix, bandwidth saturation has never been an issue. I have a TP link AX73 router as backup and will only be deployed once there is constant signal dropping for wifi devices (don't trust the claimed wifi connected devices- will not even reach there. Same with the Mesh).

So how to make sure priority is given to the NAS? I've given QoS preference to the NAS. I do notice that OD backup/download to any PC wired or not is slow, like will not saturate the bandwidth. Or there is nothing else I can do as maybe there is throttling from network provider side?

1.Device congestion

2. Wifi drop speed when penetrating obstacles
Especially 5ghz high speed connections

There is nothing u can do for the speedup for this type of usage.
If the file that you are syncing/downloading is very huge amount of small size file(like less than 10mb,then the speed slower for syncing those file is normal)
It has to download the file one by one.

Or if most of the file is large size volume,then u might check is that any hdd speed throttling issue.

My previous/current use case is syncing 1+ TB videos from google drive with "Cloud Sync",the speed is quite fast to complete sync.