Solar activity is currently low, but large sunspots still appear from time to time.
Literal
Current [genitive-の] sun [genitive-の] activity [topic-は] subdued [copula-ですが], even-so sometimes large sunspots [subject-が] appear.
An astronomy observation. 太陽の活動 ('solar activity') and 黒点 (こくてん, 'sunspots,' literally 'black spots') are science vocabulary. 低調 (ていちょう, 'subdued / sluggish') is a な-adjective describing low levels of activity. それでも ('even so / nevertheless') introduces the contrastive second clause. 現れる (あらわれる, 'to appear / to manifest') is the intransitive verb for things coming into view.