RT-AX86U PRO with OpenVPN has terrible VPN speeds

[Hometeam]

I'm using OpenVPN with Merlin 388.2 on my Asus RT-AX86U PRO and only getting 20-50 (on a good day) Mbs. I pay for 300 Mbs and I get that consistently if I use the ISP modem directly with no VPN.
When using VPN I connect to servers in North America but am located in Europe.

Before buying this router I had a desktop app installed from Mullvad (VPN provider) and I would get 50-90 Mbs when the VPN was turned on (Europe to North America). If I connect to servers within my own country while using the desktop app I get 120-150 Mbs. This was fine I guess, I accept that using a VPN will reduce speed by half, and even more the further away the servers are. But to be getting 20??? That's a joke, especially since I was getting more with the app.
The CPU cores in the router GUI don't ever seem to get overloaded, so I don't know why my speeds are much worse. The whole point of getting a router was to get better speeds than with the app...

Did I configure something incorrectly or is the problem caused by my VPN provider? Ultimately I would be happy with 100 Mbs using the VPN on North American servers. Is this even possible?
Before trying a different VPN provider is there someplace I can tinker on my end to see if I can get improvements?

 

[abidarwish]

Wireguard is a better VPN than OpenVPN. Try it.