There are several ways of varying complexity - each has a 'best use' scenario. In this situation, since the outline is clear of anything else in the vicinity and relatively simple, I would use the Extract Properties tool |CC2KEEP| to set the active properties to match the land, and then break that polygon open by snipping a small piece out of each side of that neck using the break tool |CC2BREAK|. Then I would right click the Fractalise tool |CC2FRX| and use "Path to Polygon" from the menu to convert both the resulting bits of polygon back into separate polygons - one at a time.

This is slightly out of date at the moment as I've been a bit busy lately, but this is a wall of links to all the annual issues. Hopefully you will be able to see what you are looking for there, and be able to make a shortlist of the best annuals for the purpose

https://forum.profantasy.com/discussion/10366/cartographers-annual-all-the-issues-linked-in-one-place

To use TRACED you need to have a silhouette shape. For example, if you have a land shape you particularly don't want to have to draw all over again in CC3 it is easier to use one of the free bitmap editors, like GIMP, to select and delete the oceans and (I thought this was necessary, but apparently not) turn the rest black...

The example in this blog isn't a silhouette, so maybe you don't have to go that far - only remove the oceans and leave that part transparent. There's more information on exactly how to do this here:

That's a bit strange!

Well, this being CC3+, there are always several ways of doing a thing.

Instead, click the open folder button just under the right hand end of the Options button and navigate to:

[The drive where you have everything installed]:\ProgramData\Profantasy\CC3Plus\Symbols\Dungeons\DD3\DD3 Color, and double click the Vegetation.FSC file.

It's behaving as expected on my machine - slower than a bitmap style, but no slower than my other test map.

I'm not getting a 5 second delay, though. Maybe that's because you've replaced the trees?