[Bug] Co-op has not functioned in months

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Sorry, bit of a luddite here - can’t figure out a way to open the logfiles to check which is the right one (and probably wouldn’t understand what I’m looking at anyway).
My last attempt was several weeks ago - based on the earliest save backup I have for the game I started for the attempted co-op session - I believe I have identified the most likely relevant logs (we made several attempts, trying with either of us hosting, which fits with there being four small logfiles).

Can anyone tell me how to send these logfiles (in case they are relevant) - I’m getting a message that they can’t be uploaded because they are the wrong type of file.