Up until last week I was using Aperture, I knew its days were numbered, and an upgrade to my computer finally killed it last week; I can't now install it on my new Mac.
If you have a clone of your disk from before the upgrade (you did do a backup before upgrading, didn't you?

), then you can simply boot from that to use Aperture when needed.
Otherwise, you could restore the backup clone to a Parallels virtual machine, which you can run from the new version of macOS. I used to regularly (and still can) run Windows XP in a Parallels VM.
I dislike the subscription model the Adobe use, so I messed around with Darktable for a few days. But the lack of documentation has beaten me, so I signed up with Adobe this evening. So I have Lightroom, Photoshop etc available to me.
Rather than succumbing to "the dark side", I use DxO PhotoLab Elite for most of my work - it really is something special.
The only thing it doesn't do that I want is clone stamping and, extremely occasionally, dropping in a part of another image, but the only time I tend to need that is when asked to take group portraits at our local elderly mentally infirm residence, where trying to get everyone looking towards the camera at the same time can be a bit tricky, so the odd head has to be "transplanted".
In which case, I go to Affinity Photo, which is a very good Photoshop clone, although it has that uncanny valley feeling about it where things are the same but look different.
Both products are buy once with costs for major upgrades, not subscription.