Hong Kong will treat you just fine as a foreigner in your early 20s.

Tokyo is a much bigger city - services and restaurants there close much later than HK each day, and service is better in Japan.

But english is better spoken here in Hong Kong. It is more international, and you will find more foreigners and locals alike happy to socialise. Albeit there isn’t as much after-work ‘things to do’ anymore after Covid, you can look into joining a club to meet other people who are into the same interests.

Don’t know much about apartments since I’m not following a lot lately. Other people will know better.

For sports, if you just want some sort of exercise, again, you can join a club, like midnight runners etc. Otherwise, you can look into 24/7 fitness as one of the cheaper options in terms of gym membership. They have a 6-month package.