How to randomly present a subset of materials out of a big set

Check out loop and merge.
You can have the different questions using different fields.

https://www.qualtrics.com/community/discussion/comment/36458#Comment_36458Thanks for your answer!
I have checked out loop and merge help text. As far as I understand, I can create a block starting with field 1 where I put descriptions, and make a loop to, for example, let participants answer the same four questions after reading the description in field 1. Then, I need to enter all the 600 descriptions in field 1 in the loop as lines, and only randomly present one line out of the 600 lines each time. If I want each participant to provide answers to five randomly presented descriptions (and each followed four identical questions), I can create five such blocks with the same loop. Am I right? If I need to do it in this way, how to make sure that the randomly presented descriptions will not be repeatedly presented in separate blocks? One possible way I can figure out is to spill the 600 into four groups (150 each) and create four blocks. But if there is another way to do this? Sorry for my further questions😂

In these times of unemployments, its nice to see that in five days you've managed to create a 100 more jobs. :-)
Anyway, you don't need to make it all that complicated.
Add all 600 in one field. Then randomize the loop order and show only 5 as per your requirement. This will get it done in one block with only one question.
However, since the number is fixed, if you want to have some variation, lets say, you show 4 to some and 5 some others, then you'll need to create a new block for each variant.

https://www.qualtrics.com/community/discussion/comment/36704#Comment_36704Is it possible to have four questions (include a Q-sort task) follow each description in the way you propose😂?

I haven't used the Q-Sort method, so won't be able to help you here.
TomG has developed a few solutions for Q-sort. I think he should be able to help you out.

https://www.qualtrics.com/community/discussion/comment/36725#Comment_36725But it is possible to have four questions follow each description in the way you propose, right😂? Ignoring my last mention of the Q-sort task...

Yes