most likely you see some warnings and issues in search console that were reported before your remake, browse through them and see whether you've resolved them (e.g. mobile responsiveness) and there is a button in the top right corner "validate fix" - click it
the other site that you mention is a bulletin board as well? or a regular site?
My website is a combination of both, a 'regular website' with carefully curated content, plus a board run on phpBB, the difference in impressions and clicks is huge (the board gets significantly fewer)