So you want to get the first-party builds of Cheogram Android from https://mboa-dev.itch.io/cheogram and you want to be notified of updates by Obtainium instead of Mitch.
No problem, we can have Obtainium do track-only here.
First get your download page link, it will look like https://mboa-dev.itch.io/cheogram/download/SOMETOKEN
Enter this link into Obtainium. It will enter setup mode for an "HTML source".
custom APK link filter by regular expression: javascript:void\(0\);
enable "apply version string extraction regex to whole page"
enable "track only"
version string extraction regex: Version (\d+\.\d+\.\d+-\d+)
version extraction regex capture group: $1
Enter the app name too so you know which item this is in your list