Not familiar with the Garmin cameras, but the issue of using motion detect while parked, and it generating all together far too many false events clogging up memory space are a serious problem.
So this is also why that mode of parking guard have always been advised against.
Some cameras now do handle it better, also motion detect, or at least storage of it, often by assigning a set size of the memory for the events, which when full will be overwritten just like the memory card in general.
But thats still a problem if your camera generate too many events, so your car can get rammed in the parking lot just after you arrived, and later when you get back the camera have generated so many false motion events that the actual crash are no longer there.
Personally i use regular video ( 30 FPS ) low bitrate, and then i have G-sensor on for actual events, this mean the camera always record but the low bitrate recording are just in among the regular files, and then if ´something bigger happen the G-sensor ( i assume i haven't actually tested this yet ) trigger a event that get locked in the RO folder, and i assume the camera step up to regular bitrate recording, but if not low bitrate are probably enough too.
This camera ( street guardian ) have a set memory space for the files in the RO folder, and when full the oldest files will get deleted too, and even if the SG camera deal in segments and not with a buffer and so save 2 X 3 minute files,,,,,, times 2 as it is a dual channel system, then the 12 minutes video in each event, well still room to plenty of events in the RO folder.
I also like the setup for when using the event button to save something, cuz unlike the buffered cameras you do not have to rush to the button to get the actual event saved in a locked state, as we talk minutes ( 3 in my case ) i can relax pull over, light a ciggy start swearing at that other idiot, and then press the event button.
Recording recular footage on my SG camera each file ( 3 minutes ) are 350 MB, where as the low bitrate parking files are just 118 MB, so even with a 128 GB memory card you are still fine, though if at all possible i would recommend a 256GB card for a dual system that is also used for parking mode.
Also i just use 1 hour on a times, as that cover all my shopping and at home i have a CCTV camera on my 2 floor balcony door aimed at my parked car in the back yard, and the timer i can always up should i need to park in a place for more than 1 hour ( 24 hours max )
Example of low bitrate parking mode, parked curbside on a road with "normal" city speed limit ( default town speed in DK are 50 km/h ) but 60 km/h here.
IMO much better than motion detect, and you capture everything and even get audio too, so really just need the G sensor to be on to tell if something actually happened.