Hello there. Here's a short guide on how to play Twitch Minecraft modpacks on linux.
As you might know, the Twitch app that offers this feature is only avaiable for Windows users.
But their modpacks are not exclusive, and can be played in any platform that supports the java edition of Minecraft.
Now, we're going to do it the easy way; We'll use the CurseForge website and the MultiMC launcher.
Since the Twitch app actually gets the modpack from the Minecraft Curseforge, the first thing we're gonna do is to go to their website, more specifically to their modpacks section: https://minecraft.curseforge.com/modpacks
If you're searching for a specific modpack, you can use the search bar:
After you pick a modpack, just click on it. A general overview with its description will be there. Below the name and the thumbnail of the modpack, you'll see a bar that contains a "Files" element. We're clicking there:
Now, click the latest file from the list (The one at the top), and on the next page, click the "Download" button. Save the ZIP file somewhere you'll remember later
You'll have to download the MultiMC launcher from https://multimc.org/. Scroll down until you see the Downloads section. There, you can pick the appropiate package (For Mint, the Ubuntu .deb file works just fine)
Once you get into the launcher, click "Add Instance" in the top bar
A new window will open. Here, you'll first pick "Import from ZIP" on the left bar; Then, you'll click "Browse" and select the ZIP file you downloaded before. Finally, click "OK"
MultiMC will start downloading all the modpack files. Once it finishes, go to the main window, click the modpack and click on "Launch" at the right bar
Now, it will prompt you to put your Mojang account credentials. After you write them down and click "OK", your account will be automatically linked to the launcher, and after a few Minecraft library download, you'll be ready to play your modpack.
It may be a little harder than using the Twitch client, but it's also better. Even in Windows, the launcher works much better, and offers much more features.
I hope this was useful. Thank you
PS: I originally wrote this topic on the Linux Mint forums