If you are talking about the front combo inputs than, yes (sort of). The XLR and Jack socket are actually two different connections which have been merged together.
The XLR inputs are configured to expect a mic level input (very low level signal) and the preamps will boost that signal accordingly.
When you connect via jack, it can accept an instrument input (fairly low level signal) or line level (high level signal). But you have to configure which type using Focusrite Control. I believe it’s set to line level by default. If you configure for Instrument input, the INST light comes on.
For general information:
Mic Level - Microphones
Instrument Level - Guitar or Bass DI
Line level - pretty much everything else (including outputs from keyboards, tablets, phones, etc.
This is a bit tricky because the normal amp input is designed for an instrument level. All of the outputs on the Focusrite are line level which is MUCH higher and will overload the input of the amp. So I don’t think it’s really possible using the Focusrite internal routing.
You could connect the output of the Focusrite to an aux-in on the amp (if it has one) but this is almost certainly not what you want, as the aux-in will be unaffected by amp gain or fx.
You are better off, if you have an amp with a line output, to connect the guitar to the amp and the line output of the amp to the AI input. If you have a Katana 50, I don’t think it has a line output, so you can’t really do that (it does have a headphone out which would work, but which would mute the amp when connected, which doesn’t sound what you want). The Katana 100 does have a line out.
Otherwise, your best bet would be to get a cheap guitar AB or ABY switch and plug your guitar into that, and the two outputs into the amp and AI accordingly. You can then switch between them with a tap of the foot. If you get an ABY switch, it can select output A, output B, or both which may be useful.
Cheers,
Keith