Hi
First of all I would like to point out that this is my first contact with Mikrotiks.
I found some Marvell 98DX3236 in stock and wanted to use them in my lab.
But I will start from the beginning

"Network Diagram"

WORLD ---> FortiGate 30E ---> 2x Mikrotik ----> 3x ESXI 1xNAS

The network is simple as can be seen in the super diagram.
There are literally 4 rules in FireWall on the FortiGate.
Typically a simple network

The FortiGate is connected to a 1Gbs network from EXATEL Then the traffic goes to the MikoTiks
The speed between the switches is as follows And this is what the speed looked like before I tried to fix the problem.... As you can see I messed something up but it doesn't change the fact that the speed is there However, when doing speedtest from Linux machines or from the nas server I get speeds from 2mb/s to 40mb/s and nothing more.
Where to look for the problem?

Do you have any tips?

I will also want to connect a Windows machine to the microtik to prevent problems with UNIX systems.

Your screenshots show that you're using built-in bandwidth test. It is a well known fact (you're excused since you're new to ROS) that bandwidth test is heavy on CPU and on many device models it itself is a bottleneck.
It is recommended to run tests using two external devices, known to be able to create and absorb lots of traffic. Many if us use a couple of PCs running iperf3.

So please explain your actual problem and don't try to illustrate it by showing some results of artificial load. This may then allow us to help you solve the actual problem.

I will also want to connect a Windows machine to the microtik to prevent problems with UNIX systems.

With this statement you're making me wonder. Personally I have much better experience with various Unix systems (lately Linux prevails) than with Windows (but I admit that it's not a black/white situation).

Thanks for the quick reply !

I'm not worried about the speed between the Switches (The fact on the screenshots does not show that the test was done between switches, not with the world) but more about the bottleneck that is between the Switches and Linux....
How come the Linux machines have a speed of about 4Mb as the FortiGate receives 1Gb traffic.

As for Windows they have not failed me yet, for that UNIXes yes.

Now I'm thinking that I had a similar case when FreeBSD was used as a router and Linux servers that were connected to this router were losing connection/packets .... then I had to disable RX and TX sum on FreeBSD