This is a super simple update for your denim jacket. Any denim jacket will do, new, old, stretch, any.
Simply take you jacket and using parcel tape, place a cross the sleeve to create a line to which the bleach won't pass. Do this to both sleeves equally and then place the sleeves into a bucket, sink (anything that you are happy to put bleach into).
Pour the bleach onto the sleeves up to the of the tape.
Leave for a good hour, up to two hours as you don't want the fabric to break down.
Remove the tape and wash. If possible air dry outside ☀️.