Thank you so much again Steven.
In continuation of our discussion, I found this post
where if I understand correctly, the developers state that by including the cosine columns from the confound.tsv file to the 1st level GLM high-pass filtering is applied (thus I conclude we do not need to apply separately high-pass filtering to the BOLD data by using another tool (e.g. afni, spm etc)).
Do you understand the same? 
Best,
pan