2023 Mac Mini M2 Pro slow read/write data speeds over local 2.5gb network. EtreCheck report included.

macOS has built-in security.

see > macOS - Security - Apple

Banish all signs of Norton from your Mac as per their directions.

see > https://support.norton.com/sp/en/us/home/current/solutions/v134746139

Startup in Safe Mode followed by a normal Restart.

see > Start up your Mac in safe mode - Apple Support

Re-test the Mac mini to Synology NAS speed.

"Norton could kill network performance that much?"

Yes! Mac OS is catlike and does not require or benefit in ANY way by installing the following types of third party apps:

• Antivirus
• Security
• Cleaning
• VPN
• Maintenance

Please locate Nortons uninstall instructions and then execute them. Then restart the computer in Safe Mode and then restart normally and test. All that Mac OS needs in order to remain fast, secure and trouble free is simply keep it up-to-date and restart your computer about 1x per week or so. Other than that please leave it alone!

Yes, that should be fine. Run a fresh EtreCheck report and scan it carefully and look for anything that says Norton its developers name. It's pretty nasty stuff and can leave parts behind which continue to pollute your computer.

Does your Synology NAS use SSDs or normal hard drives?

If it is using normal hard drives, the bottleneck is the drives and not the network or the Mac. A normal hard drive will generally have a max transfer rate between 100-150 MB/s maybe even 200 MB/s if directly connected to a computer.

woodmeister50 makes a very good point.

If fast external storage is needed to improve work flow, then get and connect an external SSD directly to the Mac mini.

https://eshop.macsales.com/shop/external-storage#drive-type:ssd,drive-configuration:single-bay-1-drive

Yup'