looking to replace 21 speed Shimano on a Rockhopper

[sg5y]

I have a Rockhopper mountain style bicycle ,not an E bike. 20 years old.Generic but good. The 21 speed was always overdone and un needed. But I like the bike and want to keep it. I prefer to travel with that bike rather than the heavy cumbersome XP4.
The 21 speed has 3 discs. I was wondering if Shimano or others have a modern 10-12 speed now that will swap in and provide as good or better smooth service.A 2 disc unit. Anyone know of anything that might fit the bill..?

 

[EMGX]

I might not be entirely clear on what you're asking, are you wanting to replace a 7 speed cassette with 10 speed and pair it with a 2x crankset? 2x crankset swap is simple, either square tape or hollow with external bearings and set your 3x front derailleur low stop to prevent chain drop. A 7 speed freehub won't work with 10 speed cassette (unless you remove one of the cogs and go with 9 speed). If you have a spin on freewheel then a 10 speed isn't compatible although there are some 8 speed spin on freewheels. Although any of these changes might be more bother and expense than it's worth just to drop the 3x chainring.