I think it's worth trying to enter Threads with my photos - I won't lose anything on it

You can lose only time, but if your blog becomes big, you'll become a real micro-influencer with potential cooperation with photo companies like Nikon, Canon, etc.

Flickr is quite old, once lively, now too many communities are dead there. 500px - I heard about it of course, but I have no idea, what's happening there.