Yes: Havana syndrome.
https://en.wikipedia.org/wiki/Havana_syndrome
"Havana syndrome" is a group of acute and then chronic symptoms reported by US intelligence and military personnel working abroad; the first reports were from Havana and thus the moniker. They are thought to be have been hit by a radiofrequency weapon: radar or microwaves. These folks may or may not feel something weird.
The original 21 events in Cuba were characterized as starting with
strange grating noises coming from a specific direction. Some people
experienced pressure, vibration, or a sensation comparable to driving
a car with the window partly rolled down.
Then they get sick and some stay sick. They might have nosebleeds. The working hypothesis is that Havana syndrome is the result of being hit by a electromagnetic radiation pulse, which might be from a handheld object like the gun requested in the OP.
On February 1, 2022, a declassified US intelligence report (IC Experts
Panel on Anomalous Health Incidents) called pulsed electromagnetic
energy and ultrasound plausible causes and said that concealable
devices exist that could produce the observed symptoms.[60]
Microwaves In 2018, Douglas H. Smith, the lead author of a University
of Pennsylvania study of 21 affected diplomats in Havana published in
JAMA , said in an interview that microwaves were "considered a main
suspect" underlying the phenomenon.[4] A 2018 study ... concluded that
the facts were consistent with pulsed radiofrequency[2]/microwave
radiation (RF/MW) exposure. Golomb wrote that (1) the nature of the
noises the diplomats reported was consistent with sounds caused by
pulsed RF/MW via the Frey effect; (2) the signs and symptoms the
diplomats reported matched symptoms from RF/MW exposure (problems with
sleep, cognition, vision, balance, speech; headaches; sensations of
pressure or vibration; nosebleeds; brain injury and brain swelling);
For your fiction you could make people hit by the weapon cough up blood or bleed from the nose, lurch around, vomit, seize or whatever works. I suspect that some people might be more susceptible than others. Some might be able to charge an attacker through the beam and take the weapon and see if the attacker likes how it feels.