Windows search does not search inside the files.

Perhaps that tutorial is out of date... no, Brink's just confirmed it should work.
In what way did it fail?

Should have given you this one:
Rebuild Search Index in Windows 10

Start with the search troubleshooter as steve 108 said, then if ok, rebuild the index as in that tutorial.

If still no luck, try Option 3 in that tutorial.

Perform the check again in Documents.

When did this start? (People usually omit the history).

You don't say what errors, alas. I will assume you followed the instructions in the tutorial correctly, lacking other evidence.

I suggest you perform an in-place upgrade repair of 20H2 which will keep all progs and data.This will reset services to default as well.

4) I have a lot of registry tweaks that I don't want to lose, not because I'm bored of going through them again, but because I don't remember all of these.

I will leave you with this. I do not know in what ways you've tweaked your system, or whether that may have led to this problem.

21H1 will NOT be a major upgrade and is simply bug fixing. I understand it will be more like a cumulative update, with 21H2 being the big one. It is therefore likely that 21H1 will not have the same effect as an in-place upgrade repair or 21H2.

As to all your registry tweaks... you MUST back up in a manner that makes such things easy to repeat, as any makor upgrade could reverse such thing.

Preparation and discipline.

I have taken care that any modification I have made had been minimal and easily repeated.

Good luck.

If content indexing is working in a folder known to be indexed by default, perhaps you can avoid an in-place upgrade repair install, especially if you mean you have problems only with folders that are NOT indexed by default.

(Remember my first test about adding a file and chekcing the number increments).

There are several factors at play here. You have to be logical.

1. Considering a folder NOT in the standard set indexed by default:
C:\Users\thana\Utils\Vivaldi\CSS

- is this folder specified to be indexed in Indexing Options?
- is the folder specified to allow content indexing? (Normally so by default)


The same applies to each individual file, and should be allowed by default.

2. Note this in Settings:


3. Is the file type specified to have its content indexed in Indexing Options?
This is why I said use txt as a demonstrator. KISS - Keep it Simple S....


4. Consider your start point for searching. Again, for now, KISS.
Open file explorer at the folder containing the file you want to find for now, until you are confident about its content being indexed.

** Indexed search is ONLY fast if everything in the file hierarchy below the point where file explorer is open is indexed.
Otherwise you will see a slow green progress bar.

Example: I have perhaps 600Gb of files on a hard drive. Everything is indexed on that data drive. I can find a file pretty much instantly with the right criteria.

Most of Windows is NOT indexed by default. So if your data is on C: and file explorer is open at, say, C: search will be slow.
Many people fail to realise this and dismiss Windows search, understandably.

phew! It's unusual for one not to be checked.. but there's a whole set of things that have to be true- and normally are- for something to be indexed.