There is no valid TLS MITM. All attempts at TLS MITM break TLS in some way -- very commonly with TLS client certificates.
Edit: You're only proxying the encrypted data and not trying to do a MITM, so this doesn't break TLS, but it doesn't do a MITM. I added this complaint as a more general statement at the top-level of comments.
It's my network with my assets and my data. Only I decide what is valid wrt to TLS on my network. The number of applications that purport to service a particular purpose but then proceed to exfiltrate substantial amounts of data that is not even tenuously related to the purpose of the application has destroyed any good will on my part.
On my network there are an order of magnitude more valid TLS MITMs happening than there are valid non-MITMed TLS connections.
Edit: You're only proxying the encrypted data and not trying to do a MITM, so this doesn't break TLS, but it doesn't do a MITM. I added this complaint as a more general statement at the top-level of comments.