Edit: I just saw:

including my Windows 11

No. Windows ships already well compressed. ~~There's no way it'll compress further by 50%.~~ Correction: Someone who has actually tried it says it can!

Also, as I mention below, backing up and restoring a full copy of Windows can set off anti-piracy tools that keep you from restoring your own copy of Windows. It can be done, either by waiting on the phone with Microsoft, or (presumably) by having an accomplished software pirate friend.

But look for the Windows tool "create a recovery disk". You'll need another separate drive than your 63GB one, but it probably doesn't need to be as big as a full Windows install.

Otherwise, yes.

Yes, if your drive has 133GB occupied, and you're running Windows, it is likely that Windows, itself, is over half of that.

I've not, personally, seen Windows, itself, occupy less than 70GB, in recent years. (Usually much more.)

So what's left, your files that you care about, is likely 133-70=63GB or less. (Probably much less. Windows is usually huge - usually around 120GB.)

Note that you can't just blindly backup the whole drive. You'll have to go find the files you care about and just back those up.

Backing up entire copies of the Windows operating system has gone very poorly for me, when I tried, anyway. Windows, itself, does not like to be relocated, because it tends to decide it has been stolen. I ended up on the phone with Microsoft waiting for permission, last time I moved a Windows install. So if I had a big enough drive to backup the whole Windows drive, I wouldn't bother.

There may be a utility for Windows that backs up just your files. Mac has had one for awhile. Something like the free tier of Crash plan would probably do a nice job guiding you to where the files you care about are.

Beware, file compression doesn't go far, today. The days when we stored our files in ludicrously inefficient formats are over.

I've only seen 10%-20% differences with compressed files, in 2024.

So, in your shoes, I would backup my files to the 63GB USB drive with something like CrashPlan. I wouldn't bother with compression since I don't think it will help much and I don't think you'll need it.

I would also accept that this is probably a one way trip. If the debloater works, fantastic.

If it corrupts your Windows install, you'll need to reinstall. You can use a recovery disk or download Windows 11 install media from Microsoft, which will take less space than a full install, but still takes space.

Personally, I wouldn't hassle with reinstalling Windows in 2024. Especially on a small hard drive. That's more work for a much worse outcome. I would switch to Debian. I'm fact, the first time I switched, was so being new life into an older computer.

Debian does most of the same things, takes dramatically less space, doesn't grow in size over time, is completely free, and is now much easier to install than a Windows reinstall. (Neither is pure sunshine and joy, but I would rather search for correct UEFI settings for 15 minutes than wait on hold with Microsoft for an hour.)

However you do it, resurrecting an old computer that Windows has mucked up is totally worth the effort. It's easy to forget how faster a Windows computer was when it was new.