It used to be (many versions ago) that if I was drawing with the pen tool, all I had to do is double click my last point, and it would end that graphic, leaving it open, and leaving the tool ready to draw another line. Now the only way to stop seems to be to hit return (which is awkward since I am right handed), go hit another tool, or use a keystroke. All of these take more time and break my train of thought.

Image trace to create smooth gradient fills instead of banded swatches

When using the eyedropper tool on a line, I would like the arrowheads from the line I am imitating to be applied to the selected line. I don't want to scroll through all the arrowhead options for every line! If I apply it once, It'd be so much easier to eyedrop that same feature on all the other lines I need it for.

This is something I would use for my job while making tech packs every day! I have arrowheads on the ends of dimensions and callouts.

Was present in earlier AIs. Helpful for non-marque selecting. Increases efficiency

We have to guess if we cut a path at all and if we hit the right path.
No highlight (OK, using Smart Guides helps, but Smart Guides does nothing if you also have Snap to Grid enabled!), no cursor change.

It’s 2022, right? Clouds, integrations, Stock sales directly in files... Scissors are still used with a blindfold, in a dark room, in a midnight.

Also vote for this related issue:
https://illustrator.uservoice.com/forums/333657-illustrator-desktop-feature-requests/suggestions/36111436-make-pen-and-scissors-tools-prioritize-editing-to — Make Pen and Scissors tools prioritize editing to a selected path

ich hätte gerne das Breitenwerkzeug, um Pfade individuell jederzeit in der Breite anzupassen

Similar to a font developing tool, many lettering illustrations involve maintaining the stress of a curve while moving anchors. So with this tool, you'd be able to move an anchor point and the curve handles adjacent to the anchor would move proportionally to make the curve look similar despite the anchor moving. This could be a global setting that is enabled in preferences.

Here's a better breakdown of how the feature could behave:
https://exljbris.wordpress.com/2008/07/23/wonderful_tool_for_type_designers/

Taking these selection tools away has slowed down my work....I REGRET updating!

I used to be able to use the box selection tool to make square and rectangle shaped edits, there was a circle and pointed selection tool AND there was a straight line lasso WHY DID YOU REMOVE THIS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

This is useful when you need to exactly match the scale of two objects or especially group of objects. Say you have changed the scale in one file but have received a new file from a client that is in the original scale. You want to quickly match the scale change. If you have at least one reference line that hasn't changed, you can pick two reference points on the new object(s) and then the two matching points on the scaled file. This matches the the scale exactly. This can also be used in many other ways.
https://www.thesourcecad.com/reference-scale-rotate/

Exported CAD drawings often contain many overlapping lines.
This makes such drawings difficult and cumbersome to work with, and often makes Illustrator hang.
The possibility to select an entire group of objects and, via a tool in the Object menu, remove all lines which extend parallel to and within a certain threshold distance from another line, would be great.

For constructing objects with circles, it would be nice to have a possibility to enter the subdivision / number of Anchor Points on a circle.
All circles have 4 Anchor Points and this can be subdivided to 8/16/etc., but when we need a circle with 6 evenly spaced Anchor Points, it's quite a hazzle to get there. Why not add a subdivision field?

It would be great to be able to change the pivot point of objects while using the bounding box.
Also if you can rotate not only if you're close to the corners but by holding anywhere outside the shape.
These features already exist in Photoshop. I find it veeeery clunky to have to move between select, scale, rotate tools for simple operations that can be consolidated together into one, freeing so many hotkeys for more useful stuff.

Allow the eyedropper tool to pick up text formatting and load it to the eyedropper to paint the formatting over multiple instances without having to pick up the formatting again and again after each application currently.

This exists in InDesign. So this is definitely possible.

Sometimes I would like to just use the eyedropper for fill color instead of having it match everything. It would be cool if you have individual eyedropper tools for fill, stroke, font features, and one for everything.

When editing Ellipse Properties in the transform palette, it's be great to be able to turn off the radiuses in the ellipse, enabling a live shape which is an arc. At the moment you are limited to filled/joined sections.