I don't use GoodReader, so can't say if it's exactly the same. But as of iOS 13, the Files app now supports directly connecting to external servers. SMB for sure, but can't find a definitive list of supported protocols.

You can also use Files to directly browse and access files from third party cloud services, although it requires you to download the service's app first[1].

[1] https://support.apple.com/guide/iphone/connect-external-devi...

Perhaps iOS 14 is better, but the iOS 13 Files app is not a great SMB client. It doesn't deal well with intermittent connectivity, e.g. remote hosts connected by VPN, or USB wired ethernet. When it gets confused, the only solution is to reboot the iPad, as restarting the Files app is not enough. Unlike GoodReader, the Files app does not have bidirectional sync with remote servers.

I came across the feature while using a beta of iOS 14, so can't speak to whether it's improved since iOS 13.

But my use case has involved connecting to a remote host over a ZeroTier[1] VPN, using an iPhone 6S. I haven't experienced the scenario you mentioned; most problematic issue I've had is sporadic latency spikes during folder navigation. I haven't really done any true stress testing of things, but it's handled transitions between wifi and cellular network without any noticeable issues.

It’s the same as in macOS, which hasn’t been good for years. Is it not just Samba? Did they write their own implementation of SMB?

No idea on implementation, good point that it's possibly reused code from macOS. But if various iOS apps have stable SMB clients, surely Apple can afford one? There's a possible business conflict between Apple's high prices for internal flash storage and their support for external storage.

Don’t forget Apple’s other conflict of interest: paid iCloud storage.

True, especially with the new Services bundles.

Wait so does that mean I can plug and SD card reader or other usb mass storage device into my phone and copy files directly without a third party app?

That was news to me until I pulled up that support article to add to my post, but looks like it!

Looks like there are two different USB adapters Apple sells, and the product page for this[1] one mentions it can be used for quite a few USB devices, including "USB peripherals like hubs, Ethernet adapters, audio/MIDI interfaces, and card readers for CompactFlash, SD, microSD, and more."

Biggest issue for both external HDDs and other devices appears to be power delivery, which can be alleviated by using a drive with external power or leveraging a powered USB hub between the phone/tablet and the USB device.

[1] https://www.apple.com/shop/product/MK0W2AM/A/lightning-to-us...

Yes, using Lightning-to-USB adapter, at least for apps which support the iOS 13+ Files app.

Several apps (nPlayer, InFuse, LumaFusion) also support Samsung iXpand lightning/usb flash drives natively. With native app support, files can be played directly from the flash drive, without copying to the iPhone.