Intercepting the Toniebox (client cert auth)

[SciLor]

I am currently working on intercepting the traffic of a Toniebox. I came over the SHA-1 problem, but the box stops the connection after "Change Cipher Spec, Finished" from the server with "Alert (Level: Warning, Description: Close Notify)".
What should I do, to identify the issue?

Important data about the Toniebox
-Custom CA (valid from 2015)
-Client Cert Auth (private key/client cert)
-Box starts in the past (no internal clock so it uses 2016 or so?
-Box gets the current time over the payload
-Uses SHA1 signature algos (need to use mitmproxy v8)

What I have done:
-Set up a VM with Ubuntu Server 22.04.1 LTS
-Set up iptables etc. for Transparent mode
-with faketime started mitmproxy 2015-12 to create a CA that is valid from that date.
-installed OpenSSL 1.1.1l (just in case it matters for the sha1 signature algos)
-set up a WiFi with a VLAN and DHCP Server with a fixed gateway that points to the mitm-vm
-created a client.pem with the (private key/client cert)
-installed the ca from mitmproxy to the box

./mitmweb --mode transparent --set client_certs=/client.pem --ssl-insecure

10.12.0.130:52833: client connect
10.12.0.130:52833: server connect 52.57.169.28:443
10.12.0.130:52833: client disconnect
10.12.0.130:52833: closing transports...
10.12.0.130:52833: server disconnect 52.57.169.28:443
10.12.0.130:52833: transports closed!
10.12.0.130:52821: client connect
10.12.0.130:52821: server connect 168.119.210.56:443
10.12.0.130:52821: client disconnect
10.12.0.130:52821: closing transports...
10.12.0.130:52821: server disconnect 168.119.210.56:443
10.12.0.130:52821: transports closed!
10.12.0.130:63524: client connect
10.12.0.130:63524: server connect 3.76.59.228:443
10.12.0.130:63524: client disconnect
10.12.0.130:63524: closing transports...
10.12.0.130:63524: server disconnect 3.76.59.228:443
10.12.0.130:63524: transports closed!

EDIT 2022-12-30 14:35: I think there is already a problem with the certificates notAfter/validBefore. But I struggle how to modify the certificates with a plugin