I have 2 server that's located in the same LAN network.
But I only have one network and one mikrotik router.
I need to access both server from outside (internet) with something like nginx in Linux, eg:

www.someexample.com ---> forwarded to IP 192.168.88.100 (SERVER 1)
www.otherexample.com ---> forwared to IP 192.168.88.200 (SERVER 2)

Is this even possible in Mikrotik? and how do I do that ?
Thank you in advance

No.

Well maybe with L7 rules but I don't think so.

And its not best to put reverse proxy in a router. Its not an all-in-one box, its a router.

If you have control over both servers (nginx or apache) set one as the primary, and create a virtualhost for the other and reverse proxy from server 1 to server 2, so 80,443 can be forwarded just to server 1 and both will work.

My network I run different apps on different VM's - and I run a VM just for reverse proxy with all my sites for my NAT to punch through to.

I wouldn't do, except maybe for some light hobby use, but it's possible to misuse built-in web proxy (only for http, not https):

https://wiki.mikrotik.com/wiki/Multiple_Web_Servers