Template downloads failing after update from EE5 to EE6

[contamine]

I am seeing error messages post-update from EE 5.x.x to EE 6.4.6 AND 6.4.7 on multiple sites running on a Dreamhost server. Specifically, the template download function fails and shows a series of error messages and certain front end pages yeild a separate set of error messages. The problems go away if I revert back to PHP 7.4 from PHP 8.x. All add-ons are up to date.

WHEN TRYING TO DOWNLOAD TEMPLATES (OPERATION FAILS COMPLETELY):

Deprecated
ZipArchive::open(): Using empty file as ZipArchive is deprecated
ee/ExpressionEngine/Controller/Design/AbstractDesign.php, line 331
Severity: E_DEPRECATED

Warning
Cannot modify header information - headers already sent by (output started at ee/legacy/core/Exceptions.php:120)
ee/legacy/helpers/download_helper.php, line 54
Severity: E_WARNING

WHEN LOADING CERTAIN PAGES ON FRONT END:

Deprecated
ctype_digit(): Argument of type bool will be interpreted as string in the future
ee/ExpressionEngine/Addons/channel/mod.channel.php, line 4187
Severity: E_DEPRECATED

Warning
Cannot modify header information - headers already sent by (output started at ee/legacy/core/Exceptions.php:120)
ee/ExpressionEngine/Boot/boot.common.php, line 475
Severity: E_WARNING