Draw out your entire audio rig. Where does each mic go? Where does the remote audio go? Etc.
Then draw another line from each speaker that you have to each mic that you have. That's acoustic feedback.
Also when you're drawing it out, keep in mind that when OBS picks up a speaker, headphones, etc. as an audio source, that includes EVERYTHING that goes to that device. So draw OBS's tap *after* everything gets combined. That might also create a feedback loop.
Any time you have a complete loop in your diagram - you might have to look for a while to find it - that's a possible echo if the delay involved is long enough to notice. If it's not enough delay to notice, it'll "ring" like you might have heard a sound system do. Same thing.
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If you use the meeting system like it's supposed to be used - laptop mic and laptop speakers, for example - then there's an echo canceller involved there, that eliminates that feedback. So you don't have to worry about that.
But your end, with OBS, has too much else going on for the echo canceller to work. So you have to draw it out, look for loops including both electronic and acoustic, and be ready to turn something down or off to stop a misbehaving loop.