OK, so I figured it out on my side, so I want to share my experience for others.
I ran into trouble because LineageOS wiki said that it's great idea to flash a recovery image onto boot partition or because of faulty twrp-3.7.0_12-0-payton version. In result bootloader was corrupted and it behaved strangely. It said there's an issue with selecting A/B slot and when I thought I figured it out I was experiencing fastboot "sending" stuck, also getvar was not returning any information. I also tried to switch USB cables or connect phone via USB hub. No luck.
I was about to accept I messed up and my boot will never recover then I thought that my Linux machine I'm working on is a Manjaro I have issues for some time, so I decided to use Windows 10 instead. I installed Android platform tools and Lenovo's Rescue And Smart Assistant for fastboot drivers. That was it! With this setup finally fastboot talks like it should! I get information from getvar and sending commands/files is working too. I downloaded stock ROM and executed commands sequence from
https://kfhost.net/firmware/motorola. I was at home!
So try different environment and do not use Linux Manjaro, try Arch instead. ;-)