WordPress highly recommends using the latest version of its core and the plugins. Although I do not have the exact solution for you I suggest you switch the Affiliate plugin as you have mentioned that it’s not updating since March 2019. Note that, if you delete the plugin then Affiliates may not work, until you use another solution that can make those previous affiliates workable.
From 2019 to today, if you check the WordPress recent releases it’s updating rapidly and it’s the plugin author’s job to keep the changes in mind and update the plugin accordingly from time to time to make the plugin work smoothly.
That’s why it’s better to switch to another solution that can give you similar features and to recover the affiliate quickly you can search for the solution which can give you the export of the previous data.
There isn’t such a plugin that I can recommend because regarding affiliate plugin my knowledge is not enough.
I hope this can help you on some level.
Thank you for taking the time to respond to my query with such a comprehensive solution.
You have been very helpful.