default or selected kernelversion does not have config value CONFIG_NET_DSA_TAG_8021Q.
Result is shown for kernelversion 6.9.2

Tag driver for switches using custom 802.1Q VLAN headers

modulename: tag_8021q.ko

configname: CONFIG_NET_DSA_TAG_8021Q

Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Distributed Switch Architecture
└─>Tag driver for switches using custom 802.1Q VLAN headers
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
Unlike the other tagging protocols, the 802.1Q config option simply
provides helpers for other tagging implementations that might rely on
VLAN in one way or another. It is not a complete solution.

Drivers which use these helpers should select this as dependency.

source code: