Provide last user ignoring blanks except if only data

I have a set of 150k devices where I need to display the last person and date/time they logged onto that device. I know I can use data filters to create a column of unique SNs, and I can use MAX to find the last login date, but I have some blanks and I would like to exclude those unless there is no other user data. (For example, the last login for SN1 was blank, but yesterday a person logged in, so I want to capture yesterday's person. On the other hand, SN4 shows only blanks, so I would like it to say something like "No user info available" for those.) I know I can do an IF statement for that part, but cannot figure out how to combine if last login is blank, then go to the next one with a user, and if they are all blank, show "no info avail".

Delete ALL expected results:

=LET(A,A2:A20,B,B2:B20,C,C2:C20,D,UNIQUE(A),E,IFERROR(MAP(D,LAMBDA(x,TAKE(FILTER(B,(A=x)*(B<>"")),1))),"No User ID"),F,MAP(D,LAMBDA(x,TAKE(IFERROR(FILTER(C,(A=x)*(B<>"")),C),1))),HSTACK(D,E,F))

Another formula:

Make sure the dates and times in column C are numeric (not an alphanumeric string) and please try in F18:

Formula:

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There are some differences with the expected results and Glenn's formula.
I've indicated these differences, but I think this formula is correct.

Thanks for the feedback and rep . Glad to have helped.

If you assumes tha the last login is the first row for each device, this formula does also the job:

Formula:

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In this case its not necessary the date/time is numeric. In that case also an alphanumeric string is alowed and the formula does not return 0 anymore if so.