@Pathduck , agree and I will add some more things regarding extensions from the Chrome Store.
Check first if any of Vivaldi's own functions can cover the need, before installing an extension that does.
Avoid extensions that do not have references to the author or official page
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Read user reviews and the TOS and PP of the extension. Also ask other users in this forum, if you are not sure.
Preferably use OpenSource extensions, they usually cause less problems.
Disable extensions with specific functions that are not needed permanently, activating them if necessary, to save memory.
Avoid extensions that only point to a web page and add these better to the bookmarks or the web panel
The extensions I have mentioned above meet these points and I have experienced no problems with them in the years that I have used them.
But in general I agree with @Pathduck, to limit the number of extensions to the minimum that is useful to you