You can’t beat the price.
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Cost:
You can be profligate and blow $215 for a wired Leica remote. Or you can be frugal, and spend $6 on one of these. You will also need a 2.5mm to 3.5mm adapter, another $7. While Pholsy makes versions with several different connectors, the 3.5mm jack does not appear to be available, hence the need for the adapter.

Connected to the SL2-S.
There’s also a Bulb option – you press the button and, while depressed, slide it forward. With the camera set to ‘B’ the shutter remains open until this move is reversed. No battery is required.
Wireless option:
If you require wireless operation then something like this, which works with Panasonic cameras, will probably do the trick, though I have not tried it. Again the 2.5mm to 3.5mm adapter will be required for the SL2-S body and likely with any SL series mirrorless Leica. A couple of reviews suggest it works fine.
In use:
I’m using this for tripod macro work with my Leica macro kit where smaller apertures dictate slow shutter speeds, given the modest light output of my LED ring light. While the SL2-S’s IBIS is turned on it’s never good to tempt fate and a remote release takes out any risk of camera shake, along with use of the vibrationless electronic shutter option. (Menu->Page 2->Shutter Type->Electronic). As the Electronic Shutter is silent I also turn on the Acoustic Signal (Menu->Page 6->Camera Settings->Acoustic Signal->Electronic Shutter Sound->On). I set the Acoustic Signal volume to High as I can barely hear it on Low, a problem I attribute to anno domini. The aural confirmation assures you that you have snapped the photo.
Focus stacking:
In practice this makes for very easy use with focus stacking. You determine the range of movement of the Focusing Bellows and then, starting at one end of the range snap a picture, move the bellows a tiny bit, snap another, and so on until the other end of the desired range of sharpness is reached. The calibrated rail on the rack of the Bellows makes this easy. I find that taking, say, two dozen images this way takes but a few seconds, whereafter the SD card is off to the card reader for passing the images through Helicon Focus.
Leica Fotos – pass:
One alternative idea is to use the remote trigger in the Leica Fotos app on your iPhone, but as the likelihood of that app connecting with the camera is as likely as my emigrating to North Korea, I pass on that approach.
The result:

Click the image for a larger version.
44 images stacked in Helicon Focus.
Leica SL2-S, Leitz Bellows II, 135mm Elmar lens head at f/8,
LED ring light.
Manual focus, obviously, and ISO fixed at 400. The shutter speed was 1/3 second. The camera’s distance from the subject was varied across the whole range of the lower focus rack on the Focusing Bellows II. f/8 is the sweet spot of the 135mm Elmar, now 66 years old, for macro work, but even at the full aperture of f/4 the lens is tack sharp. Modern digital sensors make these old optics sing. Adobe RAW (DNG to Leica fans) was used in both the camera, Lightroom Classic and Helicon Focus, with only the final result output to JPG.
This makes for a simply gorgeous large print:

13″ x 19″ print, but wall sized would be just as good.