The frame Adj to be / is是 Adj,but但是 … grudgingly concedes a quality before pulling back — "(it's) … alright, but …." It's a debater's move: admit the point, then keep your reservation.
Structure: Adjective + 是 + (same) Adjective ,但是 / 就是 ……
work工作busy忙是busy忙but,但是I'm我very很happy开心。
Work may be busy, but I'm very happy.
this这件outfit衣服nice-looking好看是nice-looking好看it's just,就是doesn't不suit适合me我。
This outfit looks nice alright — it just doesn't suit me.
** Remember:** the doubled adjective concedes ("busy, sure…"), the but但是 / exactly就是 clause delivers the catch. busy忙to be / is是busy忙,but但是… = "busy it may be, but…". Note: exactly就是 here means "it's just (that)," not "is."
Watch out
- The adjective must repeat exactly around to be / is是: good-looking好看to be / is是good-looking好看, not good-looking好看to be / is是pretty漂亮.