And the last example from the article, a tetrasubstituted cyclobutane, probably tells you that the functional groups connected to the cyclobutane could alleviate some of the ring strain in plain cyclobutane.
Similarly, cyclopropane also has incredible ring strain and likely won't be found in nature, but plenty of derivatives can.
Interestingly, cyclobutane and cyclopropane do not have a large difference in ring strain (within about 4% of each other).
Cyclopropanes are well known in natural product structures.
One of the weirdest is this natural product, U-106305, which has 6 cyclopropanes. Made by a strain of Streptomyces!
https://pubs.acs.org/doi/pdf/10.1021/ja9619420
Similarly, cyclopropane also has incredible ring strain and likely won't be found in nature, but plenty of derivatives can.