Dragging files not working after macOS Sequoia 15.8 update

This is like a Finder/drag-and-drop state bug than a hardware limitation or an intentional change in Sequoia. The important clue is that the first drag in a Finder session works, but subsequent attempts leave the item merely selected: Finder is receiving the mouse-down/selection event, but the drag threshold/state transition that hands the event to the drag-and-drop system is not being triggered correctly. On macOS, dragging is handled through AppKit’s mouse-event tracking rather than simply being an extension of file selection, so a Finder process, input-service state, or third-party utility that interferes with mouse/trackpad events can produce exactly this “selected but not grabbed” behaviour.

I’d specifically test whether it persists after killing and relaunching Finder (killall Finder), and, more importantly, whether it happens in a fresh user account or Safe Mode; if dragging is reliable there, that points toward Finder preferences/state or a login item/input utility rather than the 15.8 OS itself. Also test dragging between different Finder windows versus to the Desktop, because if only one destination type fails, that narrows it considerably.

I wouldn’t interpret this as evidence that the iMac is becoming obsolete; a five-year-old Intel iMac is fully capable of handling Finder drag-and-drop, and this symptom is much more consistent with an input/Finder regression or state-management bug than insufficient hardware.

The only time I have trouble manipulating items in the Finder is when I'm using a laptop and the "Force Click and haptic feedback" Trackpad setting is enabled in the System Settings. When this option is enabled, the user must learn how to alter & hold the pressure of the "click" in order to drag the selected items. I'm unable to master this myself so I have disabled this Trackpad System Setting.

If this Trackpad setting is not the problem, then perhaps you have a macOS issue involving some third party software interfering with the normal operation of macOS, or the first operation is still ongoing. Usual third party software culprits are anti-virus software, cleaning & optimizer apps, and third party security software....none of which are needed on a Mac.

What input device are you using to drag, move & drop files...?

Our 2018 Mac mini running 15.8 has none of those issues using a cheap-o USB Logitech M-100 mouse.

There is no need to replace the 2019 27" iMac just yet or replace it with a 24" iMac.

If and when you do decide to move to a new Mac, I recommend getting a Mac mini and an aftermarket 27 or 32" display.

I tried running Killall Finder in terminal but I get an error saying no matching processes found. What commands come before it to get Terminal into a receptive state?

The event happens when I try to drag from the Finder into a text document which never latches onto an insertion point. It may be an issue with the APP I am using, iNotePad.

From there on in, no "Grabs" of files happen no matter what I am doing, which is generally trying to move a file at the finder from here to there.