Yep, @Ventura raised a good point about mic vs. line-level.
Mics need a lot more gain to be at the same level, so if it's a dual function input (mic and line) it should at least have a gain/trim control or a -20dB pad (when Line level input needs to be brought down considerably).
I've looked at the Clarett and it seems it uses those Neutrik XLR/TRS combi jacks for the inputs, where the T(R)S also doubles as an instrument input.
You probably have to choose which sort of input you're using in the Focusrite software, right? Because there's not an Instrument switch on the unit itself.
Just make sure you're NOT engaging the +48V phantom power for line level use (or for dynamic and/or unbalanced mics. It can fry a mic.)
Hardware is also safer to side with than software, generally - IME.... That said, the new FocusriteControl software platform is pure gold - and yes, it does offer input (and output) differentiation and a plethora of extremely top-drawer tweakability parameters to run your workspace/DAW, recording and monitoring at optimal levels. But that's software. I run my CaptorX's with their given XLR outs and use TRS male to jack into the rear of my Clarett 8Pre. Just saves any hiccups.
I've got pretty much everything connected out the back of my 8Pre, and as I don't like to go back there without a specific reason (cable mania), it's kinda nice to differentiate between the mic-ins versus, say, the CaptorX ins just by their socket type. I really don't like going back there if I can avoid it ?????
Anyway, glad to be of assistance - the 8Pre is a dope piece of kit. I've had mine for ages, and the preamps, the "air" feature, and now the new Control software platform - just incredible. Never had a hiccup and it gets worked hard and there've definitely more than my embarrassing share of accidental meter-blasting peaks, loop-feedbacks, and red-zone panic moments. It always came out without issue.
(a sidenote: regarding the Clarett range - VERY sensitive to clean power - keep that in mind...get a decent power conditioner to run it and all the peripherals connected to it to avoid any unwanted artifacts, RFI/EMI noises/hums, etc)
Peace
Mo