You could suppress the rule for a specific IP, or threshold it so that you get fewer alerts for it
Examples:
suppress gen_id 1, sig_id 2802104, track by_src, ip 192.168.0.54
threshold gen_id 1, sig_id 2013504, type both, track by_src, count 1, seconds 600
The first (suppress) will not generate an alert for the rule 2802104 for IP 192.168.0.54 at all.
The second (threshold) will only generate an alert for rule 2013504 at most once per ten minutes per IP.
You would place these lines in your threshold.config. Not sure if OPNsense GUI has a straightforward way to do that or that you need to dive into the CLI.
More info on thresholding in general:
https://suricata.readthedocs.io/en/suricata-6.0.3/configuration/global-thresholds.html