I wanted to make a backup of my Opera Browser profile folder, but it seemed to be too big with over 1 GB. So i searched for reasons. The Cache etc. are normal space consumptioners.

Look for yourself how big them Service Worker folders could explode!
C:\Users\Your Profilename\AppData\Roaming\Opera Software\Opera Stable\Service Worker
Mine were over 400MB!
For an Opera Browser profile backup much too big.
After DIY cleansing they got 60% off size AND Opera Browser also got 40% smaller in RAM and faster in reaction and data transfer over Internet, subjectively

It could be that many users with problems with RAM, CPU usage, Browser speed or hanging Internet should look at this case to solve them.
In my view the security vulnerability of all browsers worldwide is affected by this underestimated browser feature too. I found one case of misusing the service worker a year ago, see below.

Here is my workaround against the Service Worker "Overload".
Please amplify and correct

1. Possibility:
   File Explorer:
   C:\Users\Your Profilename\AppData\Roaming\Opera Software\Opera Stable\Service Worker
   There folders:
   CacheStorage (biggest?)
   ScriptCache
   Database
   To sort files and folders by size i use the XYplorer.

In this folders you could always read the
index.txt
to see which site (mis)uses your HD space.
So i discovered plus 100MB eg from nytimes.com, where i didn't look for years.
I deleted all at once. But this is too time-consuming for evey folder.

2. Poss.:
   Simplier with the address bar:
   opera:serviceworker-internals
   Here you can manualy click unregister per Domain.
   I cleaned all up but supposed important folders like Googlemail, Opera, etc.
   Success: More than 200 MB and 60% shrunked my Service Worker folder!
   But this won't be permanent i'm afraid.

3. Poss:
   Opera developer tools :
   CTRL+Shift+I, Application, Service Worker, Service workers from other origins.
   I did not use this.

4. Poss.:
   Deactivation of Service Worker in the Opera Browser per Addon uMatrix:
   Click on the 3 points points on top of each other to the right of On/Off: Forbid Web Workers.
   This is a stable adjustment i think.

5. Poss.:
   opera://flags
   Search for "service worker".
   Enable/Disable:

• Service worker on UI thread
• Prefetch request properties are updated to be privacy-preserving
  Could be permanent, but this seams to be too unspecific und risky for many sites who do profit from that.

Conclusion:
Options 2 an 4:
opera:serviceworker-internals
Addon uMatrix
They seem to be a good team: First delete non important and then block this permantly by an addon.
But you got to look regularly in your Opera Profile folder "service Worker", otherwise it would blow up too much.

And the problem stays that you can not simply get rid off this data waste.
Not to talk of probably important security risks.

Warning: Playing with web workers an service workers could break some pages!
Yes, for website performance or while staying offline the Service Worker might be useful and necessary, but i never read something positive about it.
Who has got sources?

What do you mean?
thx

ps: Misuse, abuse of Service Worker, Webworker!
"MarioNet use cases:
DDoS attacks, cryptocurrency mining, password cracking, obfuscating relay proxies, content distribution network, click fraud.
It seems there’s not much more you can do as an end user to protect against this class of attacks."
https://blog.acolyer.org/2019/04/12/master-of-web-puppets-abusing-web-browsers-for-persistent-and-stealthy-computation/

pps: i am not a native english speaker