The "Insert > Password" command enables you to insert / fill selected cells with unique passwords.
Increasing the length or the character set increases the probability that the generated passwords are unique.
For example, for the default settings, 8 character passwords generated for an entire selected 12 million row column
all thees passwords should be unique.
Subsequent passwords are based on the continuously generated one partial MLCG random series (~(10^18)/4 passwords).
Clicking the "Reset MLCG Generator Seeds" button starts generating another independent series.
You can use the "F3/Find > Find All > Find Duplicates" command to verify whether there are any repeated passwords.
(Please note that for the above example there might be several occurrences of passwords that differ by lower- and uppercase letters and this command will list them side by side.)
Another option is the FILTER() function with the "duplicates" filter.
Generated passwords can contain Unicode characters but non-ascii characters should be used with care as some systems (especially various recovery systems) might not support them.
Such unique text strings can be also used for testing your data models with random data.
To generate random lists of predefined strings, you can use the "Insert > Custom Series" command to load/create a list, then the "Insert > Random Data" command with that list name.