TailsOS is a nonpersistent linux distribution primarily designed for Tor. It supports x64 CPUs.
It can be found here:
https://tails.net/install/index.en.htmlTails is typically flashed to a USB stick, or burned to write-once read-many optical media. While its main use-case is secure Tor browsing, it comes with Electrum preinstalled, making it a good choice for DIY airgapped PSBT signing. Where installed to a USB stick, ideally, said flash drive would either be kept on one's person at all times, or stored in a safe location (eg: beside a seed).
To use TailsOS safely, an old laptop can be stripped of unnecessary hardware such as WiFi, Bluetooth and WWAN, hard drives/SSDs and other non-essential components for this purpose. WiFi is usually included in laptops, particularly older models, in the form of a small internal mini pcie card (see attached photograph). WWAN, where included, is usually next-door to WiFi. The cables attached to the cards run to the antennae, usually housed above the screen. You may wish to remove these, too.
For the particularly paranoid, an older laptop is recommended. You can purchase a cheap CH341a BIOS programmer and flash FOSS firmware with updates disabled, and encase both sides of the BIOS chip in a resin or similar material to prevent tampering.
Further reading for DIY airgapped signing:
https://yeticold.com/https://glacierprotocol.org/https://seedsigner.com/Tails does support encrypted persistent storage when flashed to a USB stick, but this is not recommended for a cold storage scenario. You may choose to use Tails as a hot spending wallet option, in which case saving keys to encrypted persistent storage could be an acceptable tradeoff.