Way to record the screen and audio from a different microphone?

I’m a math teacher, and with the quarantine I’m making a lot of videos for my students. So far it seems the easiest to record myself writing as I talk (because equation editors are far slower than handwriting), but I’m finding that the Pencil (and probably my sleeve) are making a bunch of extra noise during the recording. I’ve just been using the Screen Recording feature to record myself talking while I write on a (mostly blank) PowerPoint slide.
– Am I correct that the audio won’t pick up a bluetooth mic during screen recording? I can’t seem to make it happen, but maybe I’m dumb.
– If not, are there recommendations for better apps where I can record myself writing and talking without recording the Pencil noises?
Thank you!
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