I find that using any tag only get interest from these communities. If I use #Splinterlands for example, people that know about or play Splinterlands will like my post or retweet it.
The decrease in activity could be due to less hive people using twitter or actively looking for posts to retweet
The restriction of Twitter api and factual closing of POSH my be the one reason for the decreased activity. However, on my Following tab on twitter I see posts with tags - so I guess tagged posts are shadowbanned in some way or another
They could be. I feel like I heard before that some tags do get shadowbanned over on Twiter/X. but I am not sure to be honest. Personally I find not using a tag gets me less to no attention.