Hi Marc,
I have the same issue
If You leave php 7.4 You cannot upgrade
if You switch to php 8 allways the same error message: UPDATE `core_output_cache` SET `cache_expire`=0 WHERE `cache_expire` IS NULL;ALTER TABLE `core_output_cache` DROP INDEX `cache_expire`, CHANGE COLUMN `cache_expire` `cache_expire` INT NOT NULL DEFAULT 0 COMMENT 'Unix timestamp of when the cache expires', ADD KEY `cache_expire` (`cache_expire`);