a little more detail on what is StemSwap sampler, and how it works:

1) in VirtualDJ, the sampler can switch between several "banks", or collection of samples.
Since vdj2025, banks can now be "locked"/"unlocked", and can also be "regular"/"stemSwap".
You can change these properties using the menu dot above the pads.
NOTE: there is a default empty bank called "MY BANK" that is stemSwap and unlocked, so you can just select this bank to start exploring the new features.

2) when a bank is "unlocked", the pads that don't have a sample assigned, will show "Rec..".
Clicking on such empty slot, will instantly record a loop from the playing track on this deck.
Righ-clicking (or shift+pad) on an existing slot, will delete the sample so you can record a new one.
NOTE: you can change what is recorded (drops vs loop, and size of loop) in the sampler menu.

3) when a bank is unlocked and "stemSwap", it will record specific stem instead of the full track.
When played, stems samples from a stemSwap bank, will mute the corresponding stem from the playing track, effectively "swapping" the stems.
NOTE: you can change which stems are recorded in the "Record slots..." popup in the sampler menu.
NOTE2: when a stemSwap bank is selected, samples will play on the deck (being affected by the deck volume and crossfader), even if they're not stems loop.
NOTE3: you can set a bank to stemSwap to record a stem, but then set the bank to regular if you want this stem loop to play without "swapping"

4) you can organize your bank by selecting "edit bank in browser" in the sampler menu, that will open all your banks in the browser, and you can drag&drop samples between folders, or to the pads.
NOTE: there is a special bank called "PER-SONG", that lets you associate a different sample collection for each particular track. samples you drop on the PER-SONG bank will be associated with the track currently loaded, and will be recalled next time this track is loaded again. So the samples in deck A pads are the samples associated with the track loaded on deck A, while the samples in deck B pads are the ones from the track on deck B.