Hi all,

My setup
ΜΤ 8XX as a main router (wired subnet .64/27)
2 different access points (not set as bridges) in ΜΤ951's (..32/27 and 192/26)

everything is working fine with static routes, etc. i can access internet, control with vnc any device from wireless to wired and vice versa with no problem)
My main problem which remains unsolved for many years is that i cannot see devices in windows neighboorhood or in streaming apps automatically. only wired ones and cannot use chromecast (from wired to wireless). Ping works ok. Access to NAS from wireless devices is available only by typing its ip. Automatically nothing is found.

For the moment i don't want to bridge each 951 AP interface with other if's. If i do so, everything works fine.
Is there a way all these 3 subnets to "talk" to each other and appear as one ?

Different subnets mean that broadcasts don't pass router (and that's one of basic reasons to have different subnets). Many of "auto discovery" protocols use broadcasts, hence autodiscovery across routers doesn't work. Next problem is firewall on some end devices (most notably Windows machines) which blocks most of accesses from outside own network ... end device has no notion of "internet" v.s. "other LANs", it's only "us and them".
The last thing is broadcasts over wireless ... theoretically it works, in practice it's only too easy for a device to miss the broadcast. This behaviour would be actual problem if "auto discovery" process would sometimes work and sometimes fail. The reason for this being a problem is that wireless devices, if idle, mostly suspend wireless receiver (for power saving) and only start it periodically. If broadcasts are sent out during "sleeping" periods, those are missed by wireless devices. The cure in ROS is to set property multicast-helper=full on wireless interface ... the effect is that AP will translate broadcast/multicast frames to unicast frames (one for each of active clients) and send them out as usual unicast frames. Unlike broadcast radio frames, which don't get the ACK handshake, unicast frames do. Also transmitter will wait for target device to "wake up" and deliver frames to it (slightly delayed, but they'll get delivered).

Which one of the above mentioned problems is the one making your life miserable is hard to tell. Could well be it's more than one. It could be that actual reason is something else ...

Wireless broadcast/multicast has it's own problems. In many cases it is falling from 866Mbps/2S to 6 Mbps/1S (basic rate), and from 2 radio/antenna to only one radio/antenna. And from checked delivery (with retransmit if no ACK received) to just broadcast and suppose/hope it did arrive.

But here is already another issue. "Multicast/broadcast discovery of services" outside of the L2 broadcast domain. https://en.wikipedia.org/wiki/Multicast_DNS
Used in Apple devices (Bonjour) , but also for printers, Chromecast and similar Netbios over TCP for Windows domain. This does not work over routed networks, unless helper processes are in place, as IP routing does not forward multicasts and broadcasts.

For Apple and Service discovery the mDNS helper could be "Avahi". https://en.wikipedia.org/wiki/Avahi_(software)
For Windows Netbios over TCP (also named NBT), a WINS server was the helper, for having a Windows domain over routed networks. A Windows AD server (Active directory) manages even larger groups with it's special DNS entries. And the NBT ports 137,138,139 have been replaced with a protocol on port 445 for Microsoft Directory services.

Here one could think of a "mDNS server" also called reflector or repeater in the LAN network (Avahi is probably just one of them). Possibly implemented as a service in RouterOS Docker container or elsewhere in the LAN? viewtopic.php?t=186911

PS: one more on mDNS and Chromecast : viewtopic.php?t=187544