It does not. The GL-AX1800 is not supported by OpenWrt. The manufacturer forked a very old version of OpenWrt and modified it to create their own custom "OEM" firmware.
OP:
Your best bet for help with how the GL-AX1800 OEM firmware works is to ask the manufacturer. We could only guess what they have done to it.
I saw that slh noted in another thread that the switch built into the SoC on the GL-AX1800 may be similar to that built into ipq40xx targets - in other words a VLAN mess. Sorry about that if this is the case.
On ipq40xx OpenWrt devices, it is a good idea to:
a) Do not use LuCi to edit and save the VLAN configuration - change this by directly editing the /etc/config/network file only. LuCi will not save the VLAN configuration correctly for ipq40xx devices.
b) Do not modify the configuration or assignment of VLAN IDs 1 or 2 tot he WAN and LAN interfaces. If you succeed in figuring out how to set up more VLANs in the OEM firmware for a guest or other network, it would be a good idea to assign them to any other VLAN IDs. I use 10, 20, 30 and 40 for the additional VLAN ID's on an ipq40xx device for example.
These steps may not be necessary on your GL-AX1800 (maybe the manufacturer "fixed" the VLAN set up issues, if there were any to begin with?), but hopefully there is no harm in setting it up this way (i.e., hopefully the manufacturer did not change how the network file is used and you can ssh into the device to access and edit it with vi) and if the steps are necessary, they will save you a world of grief setting up VLANs.
Edit:
Your devices use swconfig, not DSA, so make sure you are following vlan set up tutorials for swconfig devices. Reading through this post and the following posts may be helpful in giving you some background on what you want to set up.
https://forum.openwrt.org/t/help-with-openwrt-router-3-dumb-access-points-vlan-setup/122123/3?u=eginnc
Once again, just be sure to not use DSA configurations for your swconfig devices.