Picasa - Life after Catalina Upgrade

I would go with Lightroom Classic. Why? First off it's almost the definitive application in the area and it has an awful lot of users. Once you grasp the interface it is quite clear, and to help you there is an astonishing number of videos on sites like YouTube that you can watch and which will help you come to grips with it. It is a very good organiser and a very good editor strapped together. It is non-destructive, like Picasa was, so you can always revert to the original. I really would spend some time on YouTube searching and watching videos, it really will help.

There are other possibilities - and many of them are also well represented on YT - OnOne Photo Raw, CaptureOne (of less interest if you're not shooting RAW IMHO), DxO PhotoLab (Ditto), Exposure X5 and so on. You do have plenty of choices. :)

Picasa has been end-of-life'd a long time. It was a freebie, basic grade app. Of course you'd have a learning curve going from it to Lightroom, LR is a far more powerful, professional grade application.

Before recommending anything, what kind of photographer are you? Shooting Jpeg? Raw? Pro? Serious hobbyist? Family smaller? Volume - how many shots in your catalog now and how many would you add in a year? Any special features you want? More organisation? More editing? Cloud?

Always remember when working with an app as widely adopted as LR: you're not the first person to have the issue:

http://picasa-lightroom.com/instructions/