After searching this forum a bit more I am pretty sure I found the solution from @MichaelEischer in this thread. Briefly,
If you specify wildcards on the command line without any quoting, then these are expanded by the shell before restic sees the parameters.
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The correct syntax would be something like this:restic backup --exclude "/opt/www/nextcloud/data/*.log"Note the quotes around the file name.
And my apology to @rawtaz, using an exclude-file would have alleviated the need for quoting the wildcard-containing paths.