Serviio

Dalgliesh was a great TV series from 1983 to ca 2005.
For some reason the series was partly remade in 2021, starring other actors and rewritten scripts.

Using Serviio 2.3 I get two identically named series. With 2.1 I could get one series named Dagliesh (1983) and the other named Dalgliesh (2021).... The latter was much more informative!

What can I do to get different series titles w/o resorting to local metadata?

There was a bug in earlier versions of Serviio that was combining two different series that had the same name into a single entry. Serviio 2.3 resolved that problem. But you must ensure your files are named correctly to be placed in the proper listing. For my two different series that caused a problem, I solved it by naming the folder for each TV series with the first year, so I have a folder with Doctor Who (1965) as the title name and another with Doctor Who (2005). Another one was The Twilight Zone (1959) and The Twilight Zone (1985). My third one was Dragnet (1951) and Dragnet (1967). You might need to tell Serviio to rescan your media folders once you've ensured the names are correct. You can make sure you have the right years by going to themoviedb.org and searching for the shows.

I do have my episodes named correctly, in both cases.

Still, Serviio 2.3 via Kodi on a Chromecast with Google TV offers two identically named entries for Dalgliesh and Dalgliesh, with no indcation of (2021) or (1983) in either entry.

Serviio 2.1 offers two entries: one named "Dalgiesh" and the other "Dalgliesh (2021)".
This is consistent with their naming in TheTVDb, which lists the 1983 series as plain "Dalgliesh" and the remake as "Dalgliesh (2021)".

TMDB seems to actually list the original as "Dalglieah (1983)" and the remake as "Dalgliesh (2021)" but all of my three DLNA compliant players see both the original and the remake as plain "Dalgliesh".

So, it seems to be a quirk or bug in how Serviio2.3 uses TMDB for metadata.
If it is a bug or quirk I do hope that Zip in the long run can and will find a fix or workaround, but meantime I'd like to find out how to fix this for my particular case. Maybe some local metadata file stored near the video files?

Never had an issue. And I have a lot of identical titles.

Always put my series episodes in folders named "Title (Year) [IMDB index]". All my movies are in a single separate folder as "Title (Year) [IMDB index}"

For example:
Vikings (2012) [tt2455488]
Vikings (2013) [tt2306299]

The IMDB index number is in the URL if you lookup the series on IMDB and starts with tt.

I cannot find the original Dalgliesh series as a self contained series on IMDB.....

On IMDB some of the original Dalgliesh series appears as episodes of a much larger series "Masterpiece Mystery!", and that wouldn't help much...

Remember, although Serviio can use the IMDB ID number, it doesn't actually use IMDB for metadata retrieval. You need to confirm the way the series is listed (both name and year) in themoviedb.org. I have found an occasional difference in the year between the two sites.

TheMovieDB does not include the year in the Name field for either version of Dalgliesh. Or any other series.
However, selecting Overview -> Main shows a splash panel with the title and there the release (?) year is shown.

So, I suppose this is a minor difference between TheTVDB and TheMovieDb, and for TMDB maybe the release year needs to be retrieved separately.

As I note above, Dalgliesh (1983) is NOT listed as a standalone series on IMDB.
Some seasons are listed as separate series and some are listed as episodes under "Masterpiece Mystery!"
So for my specific Dalgliesh problem IMDB isn't relevant.

However: I think I have found a bug. I shall endeavour to report it as such.

No, officially the release year is not part of any movie or series name, with such obvious exceptions as "1984". But Serviio can use the year in the name to help identify the series correctly. As mentioned, you can also use the IMDB ID number in the series folder name or media file name. You usually don't want to use the IMDB number on each episode, since the number is different for each episode and that makes it a bit tedious to name everything correctly. That's why I suggest using the IMDB ID on the folder for each series, and leave the ID off each individual file.

I just looked at IMDB and themoviedb. You are correct that IMDB doesn't list both series, but themoviedb does. So if you have your series files in a separate folder for each series, and name the folders "Dalgliesh (1983)" and "Dalgliesh (2021)" Serviio should identify them accurately.