Welcome to the forum @quentindavid
Looking at Duplicati’s third-party SSH.NET data with Wireshark (with help from OpenSSH moduli) saw
DH GEX Number of Bits: 1024
Increase the Secure Shell Minimum Recommended Diffie-Hellman Modulus Size to 2048 Bits says 1024 bits can be broken using sufficient computing resources. Your RPi might be at the other end of the scale, possibly unable to process that fixed modulus in a timely fashion, whereas your Intel server can handle it.
I think the moduli file is commonly pregenerated, so if you have another system you could try copying one.
There was also an SSH.NET bug, but if by Beta and Canary you mean current, the change should be in it. Whether or not the change was meant to solve this missing-moduli issue is unknown, but maybe it didn’t.
Understand debug messages from sshd [closed] might also help. Did RPi ever close? Did Intel continue?
Cannot connect via SSH (Failed to connect: Session operation has timed out) has more speculation on it.