How do I get my character to keep his momentum when jumping?

try these two while walking if you want to keep momentum fully. Ground Friction and Deceleration Walking.

you can add a bit breaking deceleration if you eventually want it to stop after a while.

For the cancel out as said on the post above you can change accumulation method to cumulative.

so this is basically how it acts on my machine atm with a blank project

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on top of this if you want to stop cancel inertia immidiately on character your can basically do a very high acceleration. However you can detect move vectors also do it manually too.

This high acceleration results in this

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