I run the RPI with Stellarmate and I have the same issue on installed mark. When I click on the Installed button, the list is empty ! But into the Data management windows the file are in the installed list.
And more for some data the download never end. I have to close the data windows and into the Data management windows the file is in the installed list.

Same issue here as described by Jonathan and Alfred a.o.. Kstars/Ekos on a Raspberry Pi 4 / Astroberry upgraded to v.3.5.5 from previous versions with (regular) apt-get upgrades.

Kstar - Data - Download New data - Install [any catalog]  will download the corresponding .kscat file but it is not marked as installed in this window
nor listed in
Kstar - Data - Manage DSO Catalogs.

However, as described by others,  the .kscat file(s) are downloaded in ~/.local/share/kstars.
I tried using the "Import catalog" function of Kstars - Data - Manage DSO Catalogs, and selecting these .kcat files I did manage to install the catalogs.
(Import catalog did not let me browse into the .local folder, so I copied the files first to a reachable directory.)

They catalogs are then still not marked as installed in Data - Download new data, but I can now search again for these additional DSO objects with the find object function.

(I do sometimes have to type the full name though before some items are visible in "Find object" - not sure if this expected behaviour or also a new issue)
(For example, after installing the Sharpless catalog, typing "SH2 3" will list a range of entries starting with "Sh2 3" but "SH2 32"will only appear after I type the full entry)
 

I believe this is intentionally designed to limit the number of queries on the database, but I can't remember the rationale for it -- perhaps Valentin or Jasem know.

Akarsh,

I think it has the opposite effect as people will keep downloading the files, thinking they are not installed, when they are.

Paul

As of today, with KStars 3.5.7, this is still not working (at least on macOS).  Catalogs I've installed are not marked as installed.  Sometimes they appear to be used in the chart, but sometimes not.  

I have yet to get the Inline thumbnail images to display.  I assume this is suppose to display images in the chart even if the HiPS is not being displayed?

The images should display independent of HiPS settings, indeed. That's what it did in the past but it's broken for quite a while now.