Quantumult supports argument "group" for additional usage. Even this is the unsupported argument of official SS-URI, Quantumult needs to follow the SIP002 SS-URI Scheme.
ss://[email protected]:8888/?plugin=url-encoded-plugin-argument-value&group=websafe-base64-encode-utf8-groupname&unsupported-arguments=should-be-ignored#Dummy+profile+name
The reason to encode the group name is for the compatibility of the SSR-URI.
ss://[email protected]:8888/?plugin=obfs-local%3Bobfs%3Dhttp%3Bobfs-host%3Dbing.com&group=Z3JvdXBuYW1l#Server-1