Here are the plugins I use regularly and the ones I consider to be the best. I recommend them and have used many of these plugins for years. Some are free, some are paid (premium) and some are ones we've written ourselves.
There's also a huge choice of plugins written specifically to enhance Oxygen. I've bought a couple of these and didn't get on with the ones I bought, so abandoned them. The sites I build are pretty straightforward and I haven't found the need to use any premium third party Oxygen plugins so far. If I do, I'll let you know.
Also, be aware that the Oxygen team keep improving the product so some features that I may have been tempted to obtain through third party addons, are no longer required.
Use when you want to control what data is inputted to posts. For example if you are wrting posts about rescue dogs, you may always want to include the dog's name, breed, date of birth, and background history. Advanced custom fields can help to make complex data entry easier for users of the site.
This plugin allows me to backup my WordPress sites to Google Drive. I love this plugin. ServMask - the people that developed it, have developed a number of different extensions. I chose to buy the Google Drive extension. I have a huge amount of storage via my Google Workspace account, so using Google Drive for backups made sense. If you prefer another storage facility then you'd buy a different extension. For example they have extensions for Amazon S3, pCloud and more. It has to be used in conjunction with their free plugin.