@dax79
Since you are new to Mikrotik devices, you should have a look at the (unofficial) Rules:
particularly #8.
AFAICR TIM (italian Telecom) provides routers which can rarely be set to bridge mode, so the idea of using another device with OpenWRT is probably the best one, but the ISP provided modem/router should be able to forward some ports[1].
If you have available a Fritzbox 7530 running OpenWRT, maybe you could still set it up as "main" router (with its own firewall), I have no idea how fast is the 7530 (nor which kind of speed your connection has), but loosely having two routers one after the another (i.e. double NAT) is not as bad as many people believe, the only sometimes noticeable issue - in some cases - can be an increase in latency, that may only affect gaming.
AFAICR in OpenWRT jargon what on Mikrotiks is called hairpin NAT is usually called NAT loopback, if you want to search info on that.
[1] Usually related info/discussions can be found on:
https://forum.fibra.click/