This was my second visit to Hanoi, however both times I didn't manage to see Mr. Ho Chi Minh's body in his Mausoleum, but was around in front and on other sites around the complex.
So basically, you're reading tips from a traveler who didn't make it inside, but for sure will next time :-)
HCM Mausoleum is within a huge space with several another sites.
When entering the area you pass an airport style security check. After that you can roam freely exploring the area. You need around 2 hours min for that, excluding the Mausoleum, which visit length depends on the queueing line.
Besides the Mausoleum within the complex is the Presidential Palace, One Pillar Pagoda, HCM stilt house and a Museum (small entry fees for the latter two).
People here review and post pics of all these together, but I'll focus on the Mausoleum, while others you can read in respective reviews.
My previous visit in 2017 was during some Vietnam holidays, so the waiting line in front was very long, some 2+ hours as I was told by police, so I gave up.
This year, in Jan 2024 I put it high on my to do list saving our last day only for that.
Unfortunately, I did not know the Mausoleum is NOT open every day. It's open only 4 days a week and some of these days only 8-11 AM. So, inform yourself beforehand if you want to enter it and see Mr. HCM body.
All other attractions on the premises are open every day, so you still have plenty to visit.