Remove gap not working on Surface Book 2 when detached in v5.10

I assume that's not something that is related to the 7+ Taskbar Tweaker v5.10 update, but to Windows 10 20H2. Do you have a way to reproduce the issue without a Surface?

I suspect you are correct.  Unfortunately I do not have another way to reproduce.

Basically, the option to reduce the gap between pinned items uses the following hack:
The taskbar has four types of items: 1 – regular, 2 – pinned, 3 – combined, 4 – temporary.
The temporary type is used for an invisible item which serves as a placeholder when an item is about to be pinned.

The tweaker hooks the function which calculates the sizes and positions of the items, and temporary replaces the type of pinned items from 2 to 4. Explorer considers type 4 to be narrower.

See the following screenshot:

With the hack, the pinned item is as narrow as the invisible placeholder for pinning on the first part of the image.

Since the option doesn't work for you, it might be the case that in your setup (maybe some variant of a tablet mode, or touch screen mode) the temporary item width is as wide as the regular pinned item width. Can you check this?

Good news -- problem solved, not a 7+ Taskbar Tweaker issue!

TL;DR this Microsoft answer details how to turn off the "Make app icons on the taskbar easier to touch" option when not using tablet mode.  In short: search "Tablet mode settings" > Change additional tablet settings > Make app icons on the taskbar easier to touch.

Thanks for the explanation -- clever trick!  I found on my Surface Book 2, when hovering with a pending pin, the gap was wider than the compressed icon when using the option to reduce the gap in the 7+ Tasker Tweaker.  With the gap reduction option turned off, the hovering pending pin took the same width as a standard icon.  This was repeatable on my P52s, as well as when the Surface Book 2 was detached (making it even wider).  Regardless, the icon spacing in my docked Surface and my P52s look to be correctly gap-reduced as I remember from the past.

Below are the screenshots taken from my Surface Book 2 with a hovering pending pin and then with the item pinned.

In running through your exercise, I noticed other things were also increased in spacing.  In particular, just about everything in Windows explorer had increased spacing.  This lead me to search and find that Microsoft added and/or turned on the option to increase spacing in this latest update.  I must have missed that in their release notes /sarcasm.

Thanks again for all the help!  I am really glad to see you still keeping this tool alive and always immediately responding to updates.  I think I'm now due for another donation ;)

Great, I'm glad that you solved the problem. The Windows spacing options are new to me as well, good to know about them.