Generally spectrum analysers are not used in the same manner as an oscilloscope, you would normally connect them to 50 Ohm sources, such as the output of a power attenuator, or where you know the expected output level, for example the feed to a diode ring mixer.
However, you can make a high impedance probe that will protect the spectrum analyser, there is a design by Marek in the files section of the TinySA group,
https://groups.io/g/tinysa/filesYou will probably have to join the group in order to view the files. The attached image shows my version of the probe, the PDF is the article by Marek. The probe is powered by 5 Volts from USB, takes a maximum input of around 20 Volts peak to peak with a saturated output level of +6 dBm, or with the alternative isolated probe an input up to 100 Volts peak to peak.
SJ