Hello, I’ve already tried a few apps as Mi Fitness and Gadgetbridge to pair Mi Watch with Murena2,
and it didn’t work. Seems to look like Bluetooth doesn’t see the device at all 
Would you please give me your ideas how to solve that issue?
Cheers.
Izabella
Regain your privacy! Adopt /e/OS the unGoogled mobile OS and online services
Of course Bluetooth pairing with a sports watch is possible. I did this two days ago with my Coros. The problem is that every watch is different.
Some watches have an option for switching Bluetooth on and off. Don’t forget a Do-not-disturb-mode some watches have. Other watches are permanently searching for a Bluetooth environment but for energy saving reasons only once per minute or similar. This means pairing can require some time.
Some watches require an action on the watch, then on the device and then again on the watch. This can be tricky and you must have a look on both devices.
It can be that your watch has no name (over Bluetooth). /e/ has an option while scanning for devices to list only such ones having a name. This option is normally on.
It can also be that your watch has already an older pairing to your phone in mind. But your phone forgot it or you deleted it there or you made a system update which deleted it. In such case it can be needed to remove the already known paring from the watch before you can establish a new pairing. This can be tricky, sometimes a factory reset of the watch is needed.
Some watches are not very powerful for energy saving reasons. I would keep the distance between the watch and the phone under 1m.