Hi.
You should first decide which VPN protocol you want to use.
After a quick tour on ExpressVPN they (at least) support OpenVPN, L2TP/IPSec and IKE2.
OpenVPN is the easiest one to use and setup. It may be also the slowest.
L2TP/IPSec is easy to setup too.
IKE2 is harder to setup on mikrotik.
Details:
The OpenVPN implementation on Mikrotik doesn't support neither LZO-Compression nor UDP. If you want to use it, you have to find out if ExpressVPN forces you to use one of these technologies. If so, you can't use ExpressVPN with Mikrotik.
L2TP/IPSec is a easy to setup and maybe a little faster VPN protocol. Due to the design of IPSec ExpressVPN forces you to use a very easy to guess Pre-Shared-Key. In my opinion if you use this key you are hiding your IP-Address and location from the servers you contact through that VPN tunnel. But if someone wants to decrypt your traffic going thru the tunnel, it is easy to do so.
IKE2 is fast and it is also a IPSec protocol. however the downsites with a weak pre-shared-key are the same as for L2TP/IPSec.
In my opinion you should try to find out if ExpressVPN OpenVPN is compatible with Mikrotik. (About LZO-Compression and UDP).
If thats true, I would go for OpenVPN. If your traffic is not much confidential, maybe L2TP/IPSec is the better way to go because it should just work and is as easy to setup as OpenVPN.
Thank you for helping me.
If OpenVPN is the slowest one I'll go with either L2TP or IKEv2 because like you said confidentiality isn't of much concern for me. I only use VPN to access Geo-blocked content so the main concern (aside from the speed) is persistence in censorship circumvention. I tried some other VPN providers like NordVPN and Surfshark but unfortunately they didn't worked for me(didn't had good speeds or didn't connect at all).
About ExpressVPN's compatibility with MikroTik, I talked with ExpressVPN's support but they said MikroTik isn't among their supported routers, so they can't provide guidance on it.
The first link you gave in your post from techshield.com is not any usefull. The setup described there is completely different and not related to ExpressVPN in any way.
The second link is very helpfull and that should be the way to go.
So try removing the setup you did before and start from scratch. (Using the second link) The way to setup a VPN for OpenVPN and L2TP/IPsec is very similar.
As you said I did reset configurations on the router and used the guide in the second link and tried to change some configurations to make it match with ExpressVPN's configurations, but again couldn't make it work(i.e blocked websites are still blocked).