Yoon Suk-yeol campaigned on reducing the size of the Presidential office and it appears moving it out of the Blue House to possibly the Defense Ministry compound is how he plans to do this:
The defense ministry compound in Yongsan, central Seoul, has emerged as a new candidate to host the incoming Yoon Suk-yeol government’s presidential office, officials close to the president-elect said Tuesday.
Yoon is pushing for the dismantling of Cheong Wa Dae, a secluded compound of the current presidential office and residence, and its relocation to the Seoul Government Complex in Gwanghwamun Square at the heart of the capital in accordance with his campaign pledges to depart from imperial presidency and better communicate with people and the press.
But critics have raised concern that Gwanghwamun, a busy downtown area, is unfit as the venue of the presidential office and its supplementary facilities due to security and other reasons.
Yoon is now actively considering relocating Cheong Wa Dae, also known as the Blue House, to Yongsan’s defense ministry compound due to its potential advantages in security management, according to the officials.
Yonhap
You can read more at the link, but the article states the Defense Ministry has enough office space to accommodate the amount of Presidential office employees Yoon plans to bring over. If this happens this will be a big win for the ROK military which will have easier access to the incoming Yoon administration.