I just updated my site to Joomla 4.2.9 from 3.11. Running php 8.0.22.
Update went fine except for two problems:
1) Category Blog menu item is not recognizing number of columns. Always comes out as single column. One place where this is visible is https://www.dev.hearthstonehealthandfitness.com/why-hearthstone/results.
2) s5_box seems to be attempting to open a box on each page, it flashes up and then disappears.
note on the ftp above, be sure to go to dev.hearthstonehealthandfitness.com.