Unlike for some other extensions, Code doesn't offer me to install a prerelease version of the Julia extension. I use the Code editor as available in the Arch Linux repos, a build of the open source part of VS Code. It uses OpenVSX instead of the Microsoft Marketplace. I have 1.86.0.

The OpenVSX site does indicate the prereleases are registered, but I can't select "Install Pre-Release Version", as it's not offered in any menu in Code.