The confusion comes from the fact that “line level” is a sort of signal standard and “XLR” a type of connector or cable that uses such connectors. So there is no “XLR” type of signal.
XLR cables can carry mic level or line level analog audio, digital audio (AES/EBU), and in rare cases, MIDI, lighting control signals, or other types of signal. So there is no one “XLR” signal standard.
Furthermore, it’s most precise to talk of devices having input and output impedances, not signals or cables. For example, a Shure SM-57 microphone that might be plugged into an XLR cable has a nominal output impedance of 150 Ohms and an actual output impedance of about 31 Ohms. You could plug the other end of that XLR cable into an A&H GL2400 mixer mic input which seems to have a nominal input impedance of 2k Ohms. But other microphones and other consoles will have different input and output impedances even though they are all sending and receiving mic level balanced signals on XLR cables.
To find the output impedance of your mic preamp, you’ll want to look at the documentation.