Not in the current builds of stable. Technically the stock Guest net (192.168.9.0/24) is a VLAN but there’s no addn’l VLAN capabilities in the GL GUI. You’re going to want to go ‘out of support/scope’ & fire up LuCI (GL GUI → System → Advanced Settings).
Make a backup beforehand so you can eventually unfvck it when things go sideways… & keep a log, topology diag. Save some sanity. Then consult the OpenWrt Wiki or Van Tech Corner’s tuts over on YouTube.