I have a working OpenWRT 21.02.1 configuration for my TP-LINK RE650. But when I try to setup VLANs as seen in the given picture, my setup gets reverted in luci.
Set up a wifi AP and log in by wifi so you don't lose contact and get reverted while configuring the Ethernet. Make a new 'admin' network for it so it's not affected by what you do to br-lan at all.
Once you are running VLANs within br-lan, you need to change the lan network interface device to access the VLAN you want instead of the general bridge. It would probably be br-lan.1 here. Other networks would be br-lan.2 etc.
Thank you, that did the trick: Using a second wifi network to avoid reverting the VLAN settings, then change from br-lan to br-lan.1 to have everything working again