I want to create VLAN trunk over WiFi to extend L2 for multiple VLANs (private SSID, guest SSID, management VLAN and else) to utility building, that is shielding half of the yard and then add AP to extend WiFi coverage past this building.

I don't want to create routed (L3) network, but extend L2, because in order to make 802.11r/k/v roaming work, it needs to be managed by the same CAPsMAN (source):

For a client device to successfully roam between 2 APs, the APs need to be managed by the same instance of RouterOS. For information on how to centrally manage multiple APs, see CAPsMAN

I previously did experiment, that solved this using EoIP:

• setup dedicated SSID for "wireless trunk":
  • EoIP is not encrypted, but WPA2 encryption for dedicated point2point SSID would act as encryption for the tunnel - protection of management VLAN,
• connected SXTsq Lite2 to this SSID,
• setup EoIP tunnel and bridged L2/VLANs through this EoIP tunnel,
• connected hAP ax³ via ethernet to SXTsq Lite2,
• setup hAP ax³ as AP for private and guest SSIDs.

I removed this setup - it was just an experiment previously. And, I had some MTU issues with EoIP. Now, I'm planning to redo the setup, and I'm wondering whether that's the best approach.

What's the "correct" way to do this in home - non-enterprise networks?

Thinking about this ...

Maybe, is it possible to just use multiple VLANs through this one (dedicated) SSID? The station-bridge mode wasn't available previously for WifiWave2 driver - when I did the EoIP experiment.

Though, I wouldn't be able to use SXTsq Lite2 (old wireless driver) with new Wifi/WifiWave2 drivers in station-bridge mode, right? I will need some wAP ac (ARM - RBwAPG-5HacD2HnD) or SXTsq 5 ac (ARM - RBSXTsqG-5acD) as a client in order to use station-bridge with WiFi/WifiWave2 drivers.

WHy not considering using WIFI ethernet also known as 60hz wifi.
Basically creates a 1 gig connection between two points that acts like an ethernet cable and called wireless wire.
You can put whatever you want at the other end, switch access point etc....
You can pass as many vlans as you like ............

https://mikrotik.com/product/wireless_wire
https://mikrotik.com/product/wireless_wire_cube_pro

WHy not considering using WIFI ethernet also known as 60hz wifi.

I want to reuse already wall mounted wAP ac on the house - clear line of sight to utility building - not adding any extra box outside on the house.

Basically creates a 1 gig connection between two points that acts like an ethernet cable and called wireless wire.

Wow, 1Gbps looks very nice!

However, my ISP is 100Mbit only yet, and the baby monitoring WiFi camera needs only few Mbits either. The high-bandwidth networking tasks would be done indoors, at the desk, anyways. So, outdoors WiFi use has relatively low needs regarding the bandwidth, and 802.11ac speeds should be able to do the job.

instead of using EoIP, use VxLAN (less overhead)
but way better to achieve the link as stated by others ... use PtP 60GHz
i maintain some of these type of links at work and they are quite a no-brainer once aligned correctly

for links below ~200m and easy alignment - wAP 60G is your friend
otherwise check the Cube 60Pro ac (which even has integrated 5GHz failover available - pre configured if bought as the wireless wire pair https://mikrotik.com/product/wireless_wire_cube_pro )

instead of using EoIP, use VxLAN (less overhead)
but way better to achieve the link as stated by others ...

Can you please share some material for VxLAN and EoIP? I can't find (decent) comparison of them.