OpenVPN server on Archer A6 v2.0 uses 1024-bit RSA keys. This is a major security flaw since they have been considered unsecure for more than 10 years. The default key length used should be at least 2048 bits.

From the OpenVPN website:

For asymmetric keys, general wisdom is that 1024-bit keys are no longer sufficient to protect against well-equipped adversaries. Use of 2048-bit is a good minimum. It is wise to ensure all keys across your active PKI (including the CA root keypair) are using at least 2048-bit keys.

Up to 4096-bit is accepted by nearly all RSA systems (including OpenVPN,) but use of keys this large will dramatically increase generation time, TLS handshake delays, and CPU usage for TLS operations; the benefit beyond 2048-bit keys is small enough not to be of great use at the current time. It is often a larger benefit to consider lower validity times than more bits past 2048, but that is for you to decide.