ONLINE Add Foreign Key

MariaDB 10.8.7

I'm trying to add a new foreign key without any FK checks or tables locked.

I tried this (with and without "GLOBAL"):

SET GLOBAL FOREIGN_KEY_CHECKS=OFF;

ALTER ONLINE TABLE `table` ADD FOREIGN KEY (`initiator`) REFERENCES `main_table`(`uid`) ON DELETE RESTRICT ON UPDATE RESTRICT;

SET GLOBAL FOREIGN_KEY_CHECKS=ON;

However, I get this error:

#1846 - LOCK=NONE is not supported. Reason: Adding foreign keys needs foreign_key_checks=OFF. Try LOCK=SHARED

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Then I tried without "ONLINE":

SET GLOBAL FOREIGN_KEY_CHECKS=OFF;

ALTER TABLE `table` ADD FOREIGN KEY (`initiator`) REFERENCES `main_table`(`uid`) ON DELETE RESTRICT ON UPDATE RESTRICT;

SET GLOBAL FOREIGN_KEY_CHECKS=ON;

However, the "main_table" gets immediately locked for many queries, with "Waiting for table metadata lock".

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If I'm disabling FOREIGN_KEY_CHECKS, isn't the ALTER TABLE supposed to be performed ONLINE, without locking any tables and without checking for integrity?