hello, I have two fttc with 50 mbps in download … is it possible using the mangle nth to add the two downloads and get 100mbps?
Yes, but… a single download using a single TCP session will always use only one of the fttc links (exceptions exist but a number of factors have to contribute for it to happen). So if you have multiple streams that will share the total bandwidth, go ahead.
so would it be enough to follow what is indicated in this wiki?
https://wiki.mikrotik.com/wiki/NTH_load_balancing_with_masquerade
Exactly, just modify the interfaces and addresses according to your actual environment.
a question arises … do you need a VPN to a CHR to appear from a single IP? Or does it work like in PCC load balance?
The VPN server on the CHR will tolerate that the client connects from another IP address unless you explicitly prevent that. For UDP based VPNs, the choice of WAN may only change if the source address changes even if you use PCC rules also for own connections of the router. And if the source address changes, the VPN will break and re-establish anyway, so it doesn’t matter whether it re-establishes via the same uplink or via the other one.
But for redundancy, I’d consider forcing a dedicated VPN tunnel via each WAN, so if one WAN goes down, you can still reach the CHR via the other one.