I'm trying to get into katana zero speedruns and I'm seeing all good runs use that version, what was changed in it?

1.06 can restart running faster
Don't think it's best to rank high. The route changes a lot. For example, the Dragon34.4 route is about 0.3 seconds faster than 34.45

However, the skip tool cannot be used in 1.06, which makes Bunker2 very troublesome. It is recommended that you back up the archive to switch to 1.05 at any time

If there is no backup, 1.06 archive cannot be used in 1.05

Allows you to reset the run from the pause menu, but the rolls are bugged, so it might not be the best for speedrunning (up to you really). The Xbox release is on 1.0.6 (with no option to switch to 1.0.5), while PC & Switch are both on 1.0.5, but u can switch to 1.0.6 on PC through steams beta branches or something. Like nightmare_king said, your save will corrupt if u switch back from 1.0.6 to 1.0.5 so make sure to make a backup if u ever want to switch back.