How do you actually use cloud storage apps on Mac? (Google Drive, Synology Drive, etc.)

Your Mac isn't broken. It's Apple's system (FileProvider) that poorly handles third-party cloud apps. Finder automatically downloads photos because it tries to generate icon previews, forcing the file to download.

Solutions:

 Stop automatic downloads: open your cloud folder in Finder, press Command + J, and uncheck "Show icon preview". Use only List or Column view.

 For heavy uploads (Photoshoots): official apps fail with large volumes. Use Cyberduck (free): it is an ultra-stable client that uploads gigabytes of data directly to the cloud without errors.

 For perfect streaming (like on Windows): use Mountain Duck (paid). It replaces the official apps and mounts Google Drive and Synology as real external hard drives, bypassing Apple's system bugs.

What you're describing is pretty typical of apps that rely on macOS's File Provider framework, but I'd also check whether AVG is making things worse.

Real-time antivirus on macOS often hooks into every file open/read/write event, and with cloud placeholders that can trigger extra downloads, slow directory scans, or failed uploads because both the AV and the sync client are trying to access the same files.

If you haven't already, temporarily uninstall (not just disable) AVG and retry a large upload. Also watch Activity Monitor while opening one of those photo folders. If bird, fileproviderd, or the cloud app itself spikes CPU or network usage before you even open a file, that's a good sign Finder is requesting metadata or thumbnails rather than the app intentionally downloading everything.

It's not as seamless as Windows because the integration model is different, but upload failures and very slow transfers aren't normal, so I'd investigate third-party interference before blaming either the Mac or the cloud provider.

Instead of doing it folder by folder, open a Finder window, press Cmd + J (Show View Options), uncheck "Show icon preview", and then click the "Use as Default" button at the bottom. This should apply the rule to all folders, preventing Google Drive from automatically downloading everything.

If SMB over VPN is too slow (understandably, SMB really suffers from latency), you might want to consider enabling the WebDAV protocol on your Synology. It is much better optimized for remote connections compared to SMB, and both Mac Finder and apps like Mountain Duck support it natively. This allows you to access your NAS files remotely much more smoothly without having to use the official Synology Drive app.

szerwony wrote:

I already pay for Google and I own Synology NAS, so I won't switch to iCloud or OneDrive. Google and Synology work perfectly on my Windows PC.

If you are using third party apps to sync your files, then those third party apps may be the problem. Just a few years ago most of the third party cloud file syncing apps were just using generic apps made for Windows & just wrapped up to work on a Mac so they used file system access that was not optimal. People were complaining of huge performance issues with those cloud file syncing services even causing their Macs to become very slow. I think Apple may have added a public API for third party apps to better take advantage of the macOS file system for syncing to the cloud like iCloud does. I've heard on this forum that some of those third party file syncing apps may have updated their apps to work with the native Apple file system support. From what I know of many developers.....they tend to stick with the simplest option even it is not the best option so some of those apps may still be using non-optimal file system access.

I don't sync files to the cloud, so I cannot say for sure which of those apps/services may be better optimized on the Mac...I'm only reporting what I've seen posted by other more knowledgeable contributors over the years.

Keep in mind that many developers consider a Mac as a second class citizen and only grudgingly provide basic service which usually is not optimized for a Mac. That is why many apps are Electron based apps or web apps for quick easy deployment on systems other than Windows. Unfortunately the world revolves around Windows. If you decide to use another system, then you inevitably need to deal with the fact some apps & services may be different on those other platforms. It may involve you needing to find others apps & services which are better supported & optimized on the specific platform you have chosen...in this case macOS.

As far as your NAS, how are you accessing it on your network (ethernet or WiFi) and what router is being used. Also, was that changed roughly around the same time as gettin the Mac?

I have found some odd issues in local network file transfers with some routers to be quite odd to say the least, especially if you are using an ISP supplied WiFi/Ethernet gateway. I would double check network settings in both the router/gateway and on the Mac.

Also, any antivirus programs can also cause network access issues on Macs because those writing those programs simply don't understand how Macs work and end up with disastrous results or simply odd behavior.

3rd party system ‘helpers’, ‘cleaners’ and ‘protectors’ do more harm than good. In fact, such products are completely unnecessary for macOS and the only ‘good’ (if you want to call it that) they do is to put money in the developers’ pockets. For the user, they offer only harm…and if that is limited to harm to your bank account, then count yourself lucky.

szerwony wrote:

AVG antivirus. I will check it.

3rd party virus apps (and "cleaners") produce obscure errors and should be avoided. macOS built-in protection is all you need.

The problem is not Apple's file system as stated above. The problem is the 3rd party apps.

I use both iCloud Drive and OneDrive on a daily basis between multiple Macs and PCs.

I've had no problems as you describe.

Note that if you are using the Apple Photos application, your Photos databases must be stored on a local drive that is formatted using APFS or HFS+ (Mac OS Extended). Storing a Photos database on a FAT32 drive, or on a NTFS drive (if you have installed extra software to allow writing to NTFS volumes) may corrupt it.

If you want to synchronize photos in a Photos database through iCloud, you do it by turning on iCloud Photos – not by storing your Mac's system Photos Library in iCloud Drive. (Loose photos can be stored in iCloud Drive.)

iCloud is a synchronization system and is not really intended as additional storage for your documents, pics, music, etc. Apple assumes that everything you put in iCloud will be available for synchronization across all your connected iDevices. Because your Mac might have a lot more storage than your phone it doesn't assume that if, say, you put 500GB of files into iCloud you want to instantly synch them with your phone because the phone might not have enough storage. That's why it things don't automatically download and stay on your devices; if you press and long-hold a file or directory you can select "keep downloaded'. Apple would probably say that there's no need to do this cos you can just download the file when you need it, but their devs probably don't live in a place where a good mobile signal is indicated by 2 bars and an "E" at the top of the phone.

File download and particularly upload speeds to iCloud are on the slow side of glacial in my experience and there's not much you can do about it. Some say that iPhones and iPads are designed to be left on charge overnight cos that's when they do the bulk of search indexing, file uploads and other housekeeping - but it's not the case in my experience. If there's a file I know I'm going to need on my iPad in the next couple of days I mail it to myself because iCloud isn't reliable enough.