On Tumbleed an Leap 15.4, mosquitto does support MQTT v5 according to its man-page

man mosquitto
```
...
MQTT SUPPORT
       Mosquitto supports MQTT v5.0, v3.1.1, and v3.1.

   MQTT v5.0
       Mosquitto provides full MQTT v5.0 support, but some features are not used .directly.
...
```

and help-string
mosquitto --help

```
mosquitto version 2.0.10

mosquitto is an MQTT v5.0/v3.1.1/v3.1 broker.
```


The package description, however, still does say it only supports v3.1 and v3.1.1.

zypper info mosquitto
```
Loading repository data...
Reading installed packages...


Information for package mosquitto:
----------------------------------
Repository     : Main Repository (OSS)
Name           : mosquitto
Version        : 2.0.15-1.5
Arch           : x86_64
Vendor         : openSUSE
Installed Size : 854.2 KiB
Installed      : Yes
Status         : up-to-date
Source package : mosquitto-2.0.15-1.5.src
Upstream URL   : https://mosquitto.org/
Summary        : A MQTT v3.1/v3.1.1 Broker
Description    : 
    Mosquitto is a message broker that implements the
    MQ Telemetry Transport protocol versions 3.1 and 3.1.1. MQTT provides a
    lightweight method of carrying out messaging using a publish/subscribe model.
    This makes it suitable for "machine to machine" messaging such as with low
    power sensors or mobile devices such as phones, embedded computers or
    microcontrollers like the Arduino. A good example of this is all of the work
    that Andy Stanford-Clark (one of the originators of MQTT) has done in home
    monitoring and automation with his twittering house and twittering ferry.
```