#1 Enable the feature

Go to the following address, set the feature to enabled and restart vivaldi.

vivaldi://flags/#password-import-export

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#2 Export your passwords

Go to the address

chrome://settings/passwords

You will see two new buttons to save and restore your passwords, your OS credentials will be asked to do so. Then just choose the right filename and a folder

(keep in mind that the exported .csv file will include passwords in clear text, so better to keep that file in a safe place, possibly protecting it with a master password).
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#3 Restore your passwords

When/if needed just repeat the step #2 (obviously step #1 as well if you are using a fresh install), choosing import instead of export

That's all.

I believe that many users will welcome this mini tutorial