From a technical standpoint, there shouldn't be any issues, as long as you make sure that external drive gets the same drive letter every time, if that ever changes, CC3+ will give errors on startup, and won't be able to find menu files or anything.

From a performance point, loading files over USB is slower. Now, CC3+ does caching, and things like computing effects doesn't load files by itself, but for example zooming may require higher resolution files to be loaded, which will be a performance hit.

As for performance, and external drive is far faster than a USB stick (assuming said external drive is an SSD, but you get some nice external drives that almost looks like a large USB stick, but with a M2 drive inside, and these are quite fast.

Windows also have different caching modes. If you set your drive to use a memory cache, performance will be better, but it is very important that you don't just yank it out in that case, but use the "safe removal" option like you always had to do in the old days. Windows switched to uncached writes a while back (at least for USB sticks, I actually don't remember the defaults for external drives) because people always forgot the safe removal thing, and corrupted their drives because they though they could remove them once the copy dialog was done, but this does mean worse performance and should really be enabled on an external drive you actually work on.

No, not reinstall CC3+ itself, but the latest update (Currently update 27). The update fixes things not just with the core CC3+ install, but also updates files from the add-ons which is why it should always be installed after installing an update (or at the end if you install several in a row) even if you have installed it previously.

That is a simplification of how things work though. Not all tasks can be parallelized (and this holds true in new modern 64-bit software too, there are many cases where you simply cannot start calculating the next step before you know the result of the previous calculation), so even if a program uses multiple cores, there will often be times where there is a longer running task running on a single core which needs to finish before more cores can be spun up with other tasks. But that doesn't mean that it doesn't utilize multiple cores in a good way.

For a simple example, if half the workload can be hugely parallelized, but half needs to run on a single thread, it still halves the execution time compared to running on just a single core, even if the other cores seems idle a lot of the time. This can happen because the parallelizable workload get split all over the cores, so with 8 cores, the computer will chug through those parts much more quickly. Of course it would be nice if it could use all the cores all the time, but that's simply not always possible.

(Not claiming CC3+ can't be improved here, just highlighting some of the general issues with multiple cores and parallel processes)

It doesn't have anything with it being an object or not. CC3+ needs to be able to tell where the edges of entities on the sheet is when applying effects. When CC3+ computes effects, it makes a render of the complete stack of sheets up to and including the current sheet in the rendering process, and then compares the image it gets with the same pass done with the below sheet. Pixels that are exactly the same between the two renders will be areas where the latest sheet didn't have any entities, so we are seeing the sheet below through these points, while pixels that have changed represent areas that the current sheet covers. Edges are identified as borders between where pixels change and not. Effects are then applied to the image, and CC3+ continues one with the next sheet in the stack

This may seem complicated since CC3+ should just know where the entities are, right? Well, that would be the case if it wasn't for the effects, because once you start applying these it gets quite complicated and CC3+ needs to actually do these renders to calculate where the effects stretches to. And multiple effects on a sheet also interacts with each other, making this quite complicated.

So, this isn't some arbitrary rule that can just be turned off. Changing this would mean completely changing the way CC3+ renders the drawing.

I won't call it a big problem, as most of it is taken care of quite quickly, but it has been a bit of an increase in spam lately.

One of the problems is that most of those aren't actually bots, but actual people in poorer countries who work cheaply, and it is very difficult to prevent live humans who can read from creating an account, log in, and post something, without also making it an unpleasant experience for new users, something which is very important to me not to do.

There are rate limits in place for how often people can post, which is quite effective in preventing them from filling the forum front page with spam, you may have noticed it is always just two posts. Back in the old days, spam didn't happen quite as often, but several times I had to clean out a spam-attack of 20+ posts filling the entire first page.