Could we actually observe this

Yes. We could look at anything outside of the 'shrinking bubble' and measure it, and notice that it's all becoming 'larger'.

We would use telescopes of various kinds to measure the apparent angular size of all things outside the bubble becoming 'larger' and then use trigonometry to figure out their actual size becoming 'larger', whilst things inside the 'bubble' would not.

Edit: let me guess you would take your raisin and put it on a triple beam balance.

No, that's how you'd measure the mass of things that are roughly comparable to human size, not how you measure the size of things.

Mass and size are not the same.

We actually measure the mass of very large objects in space via a combination of many, many different measurements of different kinds, in combination with a whole bunch of physics that would require me to educate you an amount I'd want monetary compensation for, as it would likely take weeks or months or years.

Also, if localized shrinking did exist why would it be unique to our carve out of space?

Ok so from this comment I can infer that you are yourself not in favor of the idea that we are in some kind of shrinking bubble.

I offered that as a thought exercise for you to illustrate that a localized shrinking bubble is an obviously nonsensical explanation.

You don't seem to find that a compelling explanation, so that's good, but now I have no idea how your 'are we just shrinking' explanation of Hubble's law works.

...

Do you think everything in the universe is somehow shrinking, at the same rate and scale?

If so... well, not only would that be nonsensical, but it also would not explain Hubble's Law.

Do you think that the universe is full of 'shrinking bubbles', and that the space between these 'bubbles' is immune to this shrinkage?

I'd love to see an explanation of that which does not fly in the face of what we understand about the universe.

...

You started this thread asking a question which has an actual and definite answer.

You have in this thread been given simplified metaphors which illustrate this answer from various people.

You've claimed this isn't an academic debate, when the notion of the universe expanding derives from academic study, which you don't seem to have much grasp of, as you've stated that 'we don't know much about the nature of the universe'.

My conclusion at this point is that you are being intentionally ignorant and contrarian, demanding people explain nonsensical shrinking concepts which are not occuring and are impossible, whilst you provide absolutely no explanation of anything.

If you want to learn why we believe the universe is 'expanding', go watch some astronomy 101 lectures on youtube, or take a course on brilliant, or find a book or webpage explaining this topic, or go take some community college courses or something, hell, just actually read the link I provided to Hubble's Law on wikipedia earlier.