John wrote

Update. Did a Google on slow Windows 10 laptops.
I have Lenovo 310 Ideapad, whic is excellent.

Much comes up on the web, with most saying
the same thing, like get rid of start up apps,

Thats sensible.

get rid of clutter on the disk,

That makes no sense, it isnt what slows the system down.

defrag disk,

Ditto in spades.

go into some parts of OS to enhance performance,

What ?

remove AVG anti-virus using only Defender, etc.

I did, making a difference with it now workable,
but still a lot slower than when new. I only use the
browser and OpenOffice, no games or other apps.

Which browser ? Some can slow things down a lot.

Also it is still slower booting up even before Windows has
booted, so this indicates it is not a Windows problem alone,

No it doesnt. Win does load a hell of a
lot of stuff before it allows you to use it.

although I am sure Windows is the
prime culprit in everyday running.

Its more likely to be something you are still running.

Some say fit an SSD as this will make it faster. An SSD will.

Only with some things like how quickly it
boots and how quickly it starts big apps.

However the underlying problems still are there,
with the SSD sort of papering over the cracks.

Only of you dont have enough physical ram
and its swapping a lot more than it should.

How much physical ram has that system got ?

I want the root cause eliminated.

May or may not be possible.

I have little faith in Windows considering installing
Linux, as being UNIX it is more stable, professional

Thats very arguable.

and less prone to attacks.

But those are trivially avoidable.

I am thinking of an SSD and Linux, so
with my fibre broadband I assume it
will be lighting fast to what I have now.

It wont be, particularly with the browsing.

A new Unix OS, SSD and fibre Internet
access will be like buying a new laptop.

Fraid not.

I asked if Linux word processors are "Word compatible".
I know there are many free suites available. I am any
new word processor to read and edit my old files and
not ruin the document format. Professional word
processing software these days are give away items.

Depends on what you mean by professional word processing.

Is Linux free

Most of them are.

or do you have to buy it?

Nope.

It needs to be downloaded onto an USB stick

Nope. It can be downloaded to your current win system.

or come on a USB stick.

It can do but not for free.

Your other problem is that there isnt just one Linux,
there are dozens of common ones and lots more less
commonly used ones with some radically different user
interfaces and ease of installation by someone like you.