There are lots of similar bugs being reported with PHP8 so I’m waiting this out.
I have the PH8.0 errors in my WordPress5.5.3 too (i.e. Fatal error: Uncaught ArgumentCountError: array_merge() does not accept unknown named parameters).
I’m testing PHP8.0 with Xubuntu18 (32bit machine), Apache 2.4.46, MySQL 8.15-1 and PhpMyAdmin5.0.4. Looks like I’m reverting back to PHP7.4.
