The characters in the flag appear to be "搜救 回收大队" which Google translate gives as: "Search and rescue recovery brigade"
Though I haven't found a direct link to an organization with that flag, all the references point to it being the search and rescue unit of the Jiuquan Satellite Launch Center
References
This article describing the Shenzhou 12 landing has some relevant notes.
https://m.chinanews.com/wap/detail/zw/gn/2021/09-18/9568565.shtml
The article is in Chinese, quotes below are from Google's auto translation
Bian Hancheng, deputy chief designer of the landing field system of the manned space project and researcher of the Jiuquan Satellite Launch Center, introduced that due to the large undulating sand dunes of the landing field, it is easy to block the line of sight, which increases the difficulty of search, disposal and transportation. In order to welcome the astronauts triumphantly in the most reliable, safest, and warmest way, the search and rescue team of the Jiuquan Satellite Launch Center has long woven a "world network" and trained "search and rescue soldiers."
http://eng.chinamil.com.cn/view/2021-07/20/content_10064315.htm also has this information:
According to the mission plan of the Shenzhou-12 manned spacecraft, the return capsule is scheduled to land at the Dongfeng landing site in two months. The search and rescue unit of Jiuquan Satellite Launch Center will undertake the search and rescue task of astronauts and return capsule for the first time.
As a professional search and rescue force of the aerospace field in China, the unit is mainly responsible for the search and rescue of astronaut, as well as the search and recovery of returnable spacecraft and rocket wrecks. It has successively completed several major tasks including those of the test return capsule of the new-generation manned spacecraft and the return capsule of the Chang'e 5.
The soon-to-be-started mission of the Shenzhou-12 return capsule is the first time for this unit to perform the search and rescue of manned return capsule, which is also a fresh challenge for the systems in the Dongfeng landing site.
From CNSA Watcher (CNSA = Chinese National Space Administration)
https://twitter.com/cnsawatcher/status/1438069971104436226
The search and rescue team of Jiuquan Satellite Launch Center are busy training in Gobi Desert. Today, the #Shenzhou12 astronauts have been in orbit for 90 days...
Which links to this article https://mp.weixin.qq.com/s/w4ZdI21mrJ61j_d8XTLYGw (in Chinese - again using google auto translate)
"If you want to win in actual combat, no one can run in training!" This is a sentence often heard by members of the search and rescue team of the Jiuquan Satellite Launch Center on the training ground
...
As the only professional aerospace search and rescue force in China, the lowest goal and the highest requirement set by the search and rescue team is the arrival of people in the cabin. The team insists on taking actual combat as the starting point
At the bottom of this last article is a larger graphic that contains this logo which may be a variant of the emblem on the flag (note that it's not clear that this is an "official" logo. My Chinese is not good enough to make sense of all the text in the full graphic)
(JSLC = Jiuquan Satellite Launch Center)
