four months of daily posts and almost zero replies, is this normal or am i invisible Posting Slump

Normal, unfortunately. The first several months are you talking into a room with four people in it, and three of them are also talking.

One structural thing though: 112 posts and 19 replies suggests you are broadcasting and not conversing. Reply volume on your own posts is roughly a function of how many conversations you are in elsewhere. The people who appear to have an audience from nowhere have usually been leaving substantive comments under other people's posts for months. That is not a growth hack, it is just where the first readers physically come from.

Check whether your posts end in a place where a reply is possible. "Shipped the export feature, here is a screenshot" is complete - there is nothing for anyone to add. "Shipped export, went with a queue instead of doing it inline, still not sure that was right for 40 row exports" leaves a door open, and people walk through doors.

Half my early posts were tidy little announcements. Nobody replies to an announcement.

Daily is probably the problem too. Daily forces filler, filler gets no engagement, no engagement teaches the feed you are boring, and then your good post on Thursday goes nowhere either. Three posts a week that you would actually want to read is a better trade.

Four months in I had 9 followers and one reply, from a bot. Month eleven a post about a bug I had misdiagnosed for a week did 60k impressions and brought in the first real batch of users. There is nothing clever to conclude from this except that the curve is lumpy and four months is not enough data to quit on.

Also worth separating replies from readers. My reply count is embarrassing but Plausible shows a steady 30-40 people a week landing on the site from the profile link. Loud silence and no audience are not the same thing - check whether anything is arriving before deciding nothing is.

The kind person who has replied six times is worth more than 200 likes. Ask them what they are stuck on and answer it properly. That is how the second one shows up.