Starting from Catalina only 64-bit will be allowed to run, otherwise you see a warning:
And compiling Treesheet from source code is a bit tricky. Luckily I found that in the CI worfkflow the daily builds already in 64-bit.
Here is where you can find it. Goto the actions from official repository,
and click on the latest successful build, eg: https://github.com/aardappel/treesheets/actions/runs/119194981
For unkown reason for me, the app opens default in Italian, here is the workaround that I use to force it back in English: After unzip and go inside the *.app/ from command-line:
$ cd ~/Downloads/Mac\ TreeSheets/TreeSheets.app/Contents/Resources/translations
# remove or move all other translations folders into a temporary directory:
$ mkdir temp; mv * temp/
Try open the TreeSheets.app again