Make custom Drupal 7 module / iCal library compatible with PHP 7.4 and 8

I am using a custom created Drupal module to export data from the availability calendars module as iCal. The custom module makes use of the iCalCreator library. It all runs well with PHP 7.3. When switching to PHP 7.4 I get a few deprecated function debugs and with PHP 8 I am not able to open the iCal links anymore. Deprecated function: Array and string offset access syntax with curly braces is deprecated in include() (line 56 of /.../sites/all/libraries/iCalcreator/[login to view URL]). Deprecated function: Unparenthesized `a ? b : c ? d : e` is deprecated. Use either `(a ? b : c) ? d : e` or `a ? b : (c ? d : e)` in include() (line 56 of /.../sites/all/libraries/iCalcreator/[login to view URL]). As I am using an old iCalCreator library version you need to modify this version to make it work with PHP 7.4 and 8. Or you implement the new iCalCreator library version and modify the custom module to make it work exactly like before (I need to have the same iCal output as before). I would send you the existing modules and library to test it on your own Drupal 7 system. Unfortunately I can't supply access to the production site. You just need to create a content type (Machine name: availabilitycalendar) with an availability calendar (Field name: field_availability_calendar).