NordLocker was part of Nord Security external ISO27001 audit in 2022. Of course, being closed-source software you can’t really know security fully. The biggest concern seems however to be the encryption model they use in addition to being closed source. However, for example, hosting my own cloud service while most secure really isn’t the option that would answer the reason I use cloud service.
I am not saying use it. I am saying it often gets recommended. I really do think people should do their own research on if things are best fit for them. I am having a huge issue finding actually secure solutions that are not self-hosted and FOSS or at least open source. Nextcloud which is fully hosted by service or on your own bought server space has some concerns as well.
I had it but really had to scroll to the bottom. It was also not Reddit but articles saying it was the first result. Which is kind of ironic.