magisk is mostly used these days (at least on these watches) and there are several ways you can go ahead to root with magisk. One way to do it is by flashing twrp first and then install magisk.
@Julián_Chico , there are two versions of the lem t now with different screens, so you’ll have to check your firmware version
If the firmware version ends with a D you can try this one (ported from the one below it):
But if there isn’t a D at the end of the firmware version, you should use the one shared here:
then go to this thread to get the stock firmware(top post for non D version, or last post for D version):
First off - sorry @promethian but I am hijacking your post slightly to add updated firmware
steps:
install magisk manager (Downloading Magisk App... | Magisk Manager )
through magisk manager, download magisk.zip
transfer the stock boot image to a folder on the watch
flash twrp to both the recovery and boot partition
turn on the watch and it will automatically boot to twrp
install the stock boot image
install magisk.zip
reboot and done