confusing formatting in rofi-calendar

[johnwuelk]

rofi-calendar shows the current date as bold and underlined only with version from 2018: https://github.com/vivien/i3blocks-contrib/blob/7191f887a30658a6246550f769f6682f532ad00e/rofi-calendar/rofi-calendar
But with that version Monday as start of the week is not included. And the buttons for previous and next month aren't included either. How can I make these 2 things work in this old version as well?

With the newer versions Monday as start of the week is working but the formatting neither shows the date as bold nor underlined. Instead, corrupt chars are shown around the current date. I'm using rofi 1.5.4-1 and util-linux 2.34-0.1ubuntu9 for cal which I had to downgrade. But I tried older AND newer versions as well and even in a VM on a different system- same behavior.