Rather than compromise and run Tahoe from a bootable external disk, which only reduces the risk, why not run it in a VM, where it should be safely isolated from the rest of your Mac? Before you try installing your VM, you’ll need to install a software enabler. This can be Device Support for macOS 26 beta, available from Apple’s developer site alongside the IPSW image file for Tahoe, or you can install the beta-release of Xcode version 26 instead. If you do neither, when you try to run your Tahoe VM you’ll be warned, and invited to download the enabler, but that isn’t likely to work, leaving you with an unusable VM. Then download the IPSW file from Apple’s developer site, or via Mr. Macintosh’s link to Apple, install that and run your VM.