From their responses in interviews with Indiewire, it seems that the main actors did a lot of the fight scene themselves. However, Melanie Phan is credited as stunt double to Michelle Yeoh on IMDb for the episode in question (along with 3 others) - so there were at least some stunts that she did not perform herself in the episode. Jason Isaacs also has a stunt double credited for the episode, but it is not clear they were used during this fight sequence. The interview responses seem to indicate if so, their use was minimal:
Jason Isaacs to indiewire:
When it came to shooting Lorca’s final battle, Isaacs was candid about what exactly it means to do a fight scene with co-star Michelle Yeoh, who first broke out as an international star in the 1980s and ’90s after appearing in a number of Hong Kong action films (and doing her own stunts).
“If you know you’re doing a big fight with Michelle Yeoh, that’s about as good as it gets,” Isaacs said. “That’s like dueting on stage with Stevie Wonder or something. However, when you start rehearsing things, you realize why she’s Michelle Yeoh. She can move 20 times quicker than my eye can focus, and I’m meant to look like I’m keeping up with her. So I’m begging her to slow down all the time.”
In addition, that fight training means that “[Yeoh] can make the lightest contact in the world and make it look like she’s hammering you. Me … I’m actually grabbing her arms and banging into her and bruising her terribly. So I’m feeling like a clumsy, drunken hippo fighting her, but I’m still getting to do a fight scene with Michelle Yeoh, which is great.”
Michelle Yeoh to indiewire:
“Jason has done many action stunts, and he does everything himself,” she said. “It’s like, ‘Are you sure you want to do that roll, Jason? You don’t really have to.’ He was like, ‘No, no, no, no. I can do it.’ And so he’s falling on his… It’s Jason all the way.”
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Yeoh said that the fight sequences in Episode 13 were the longest of the season, which she felt was necessary because “Jason’s character was so pivotal and important since Episode 3, and this was his send-off.”
The day they filmed the ultimate confrontation, Yeoh said, was a great deal of fun — and they had an audience. “Anthony Rapp was there, and a couple of our other actors. We all go, ‘What are you guys doing? It’s your day off.’ They’re like, ‘Oh, no. We came to watch you guys fight.'”