Having to rebuild a site after Russian hackers' ransom attempt..
Because Joomla! 3 is no longer supported as of yesterday, 17 August, I upgraded to J4 on a clean installation.
I had purchased, and had been using the Oxygen template, but find that it won't work on J4, crashing on the simplest thing, "const DS" ("directory separator" ['\' or '\']) which Joomla had been using, apparently, to distinguish between browsers running on Windows vs Mac.
Any chance of supporting a long-time customers (c. 10 years) with an update?
Will you be going through your catalog to clear out the problems with the upgrade? (I see you have 19 templates that are J3 only.)