I had the same stamp from the Ho Chi Minh City consulate. It was just before Covid, so I didn't try to get more tourist visas since then. But I doubt it would have any real implications.
Do they have legal grounds to refuse a tourist visa if you meet all the requirements listed on their website? There is no mention that you should have no more than a certain number of tourist visas in the past.
Did you see a previous thread by OP? It's the second time they haven't let him out. The first time he didn't have an overstay. They just said he had too many covid visas.
One should only get a vaccine if they are in a risk group - old, with underlying conditions etc. Otherwise it's not worth the risk of possible side effects.