Do nearly all historical dramas use the tragic ending

No there are plenty with happy or open endings:

• Sungkyunkwan Scandal - Happy
• The Story of Ming Lan - Happy
• The Legends - Happy
• Lost Love in Times - Happy
• The King's Affection - Happy
• The Princess's Man - Slightly bittersweet but mostly happy
• The Crowned Clown - Happy
• Story of Yanxi Palace - Happy (tragic / bittersweet for the SML)
• The Imperial Doctress - It takes forever and its slightly open but I'd still say Happy in the very end
• Love in the Moonlight - Happy / open
• The Eternal Love - Happy / open (The Eternal Love 2 / The Eternal Love 3)
• The Untamed - Happy / open
• Mr. Queen - Some people take it as a happy ending, some take it as bittersweet
• Splash Splash LOVE - Happy
• Sound of the Desert - Happy (tragic / bittersweet for the SML)
• The Tale of Nokdu - Happy
• Rookie Historian Goo Hae Ryung - Can't remember if this was happy or open but it wasn't tragic
• The King in Love - Happy (bittersweet for the SML)

The Legend of the Condor Heroes (1983) has a happy ending.  I assume the other versions do as well, but this is the only version that I've seen.

Thanks everyone for the reccomendations and confirming that it is not all tragedy in the subgenre.

I would say yes that used to be the case but with streaming platforms growing in China you see a lot of short and 'sweet' dramas with happy endings.