For RSTP and MRP RSTP+ connections, I reviewed the following documents:

and

However, I couldn’t find an example that matches my topology. The closest example is the topology you sent.In fact, I designed the RSTP+ and MRP configuration in the TIA Portal topology view and made the necessary settings.The point where I got stuck is as follows: RSTP+ is a feature that prevents RSTP BPDU packets from entering the MRP network and makes the MRP ring ports appear to RSTP as if they were a single port. At the same time, with the Interconnection ID, we can specify the other switch that will act redundantly in the RSTP network. In this way, the two switches connected to the RSTP network can see each other through the MRP ring, and only one of them connects to the RSTP network. This is where the problem starts. If this is the case, the topology I designed will not work, because I need both ports connected to RSTP to be active when necessary. Moreover, in my design, the two switches leaving the MRP ring will not operate in a redundant manner.

I assumed that my topology could work based on the following information: In the examples, RSTP+ is enabled on both switches in the MRP ring, and we can connect RSTP links from these two switches to external networks as we wish. (There are also cross-connections in other configurations, such as when multiple MRPs are connected via RSTP+.) For this to work correctly, only one of the ports from both switches to the RSTP network must be active. If the switches were seen as independent switches by the RSTP structure, they would keep communication open with both. However, this is not the case; they are perceived as if they were different ports of a single switch. Therefore, only one port can be active while the other remains in standby.

Thus, I am certain that RSTP+ presents both switches to RSTP as a single switch and keeps only one port active while disabling the others.Based on this, as can be seen in the diagram I sent again, the RSTP system will assume that three switches are connected to each other and will operate accordingly.

Of course, I am not completely sure.