cyclingabout.com sells an annual buyers guide for about $25. If you are in the market for a new touring bike that is probably a good investment.
https://www.cyclingabout.com/touring-bicycle-buyers-guide/I'd say from a strategic standpoint the time to start shopping for a touring bike is in the fall. You might catch a bargain on a model that is going to be updated for next year. And if you want to custom-order something fancy you probably need to get that order in by October or November if you want to be riding it next spring.
Some stuff I'd look for in a touring bike (a lot of this is "well, duh!" to the many experienced riders here, but still...):
- Stable and relaxed geometry for comfortable semi-upright riding over longer distances.
- Really wide gear range (500%+) with the lowest gear having 20 gear-inches or less.
- All the mount points for racks and fenders. Bonus points for a third bottle cage mount under the down tube and three-bolt mounts on the front fork.
- Thru-axles front and rear. Some might debate this but for pete's sake it is 2024.
I'd also add that it is worth the investment in time and money to get a proper bike fit for a touring bike. You are going to be spending a lot of time in the saddle and that is the best way to make sure that time is as comfortable as possible.
A pet peeve I have is that most bikes, and certainly most touring bikes, would do well to have oversized front brake rotors. This can make a heck of a difference on a screaming fully-loaded descent from a mountain pass. So if you can upgrade the front rotor to a reasonable size like 180mm when you build the bike you will be a happier cyclist on the Big Downhills.