From subfolder to subdomain

[SnakeEaterITA]

Hi everyone, for many years we've had vBulletin on a subfolder `https://www.mydomain.com/forum` and we are now considering moving it to a subdomain in order to keep it on an old version of PHP while the main website (WordPress) could have a more modern version.

Now the question is: is there anything I should worry about when doing this? More specifically, will this impact stuff like permalinks, SEO, plugins, etc?

Thanks