1 - I am currently playing with version 120.4.1 on my linux ubuntu, but I have no idea how to update it to 121.0 without losing my settings and maps.
2 - In addition, I try to click or start from the terminal on the "simutrans" file and it simply does not open or is it some other way to open the file?
How did you install Simutrans?
If you installed it via Ubuntu repositories, I think version 121 is not yet available. You can use the independent repository to have more up-to-date Simutrans and paksets https://simutrans-germany.com/wiki/wiki/en_Simutrans_repo_deb