What exactly is Forge and should we always use this option on a large format printer like an Epson 7900 or Canon P2100?

Just  so I understand use Forge for regular printing unless you want to print fast then use Fusion?

BTW, this is really not a complicated thing to decide.  Just use Forge.  Fact is, nobody is really going to care that it takes Forge 19 seconds to process a 13x19 print vs 10 seconds for the old Fusion.  It'll take your printer several minutes to actually print it so you have to be a real outlier for an extra 9 seconds to not be worth getting the best print quality possible.

Oh, I also wanted to mention...  If you open an old job that was saved in 2022.107 or prior, it'll obviously be set to the old "Fusion" when you load the job.  This is as intended: jobs should load faithfully to how they were printed/saved initially.  Should you change it from "Fusion" to "Forge" and reprint it?  I'd say no, unless you are just bored.  Remember, differences in interpolation methods only show up at either high magnification or with high amounts of "stretching"; that is, if you printed a really low res photo at a large print size.  Otherwise you'll need a magnifying glass to see the difference between interpolation methods.  But starting with 2022.108, I'm personally always going to use the new Forge method.  My logic is as it has always been: why not print the best possible optimized quality that is available, whether or not you need to put your nose to the paper to see the difference?

Mike