I have a class B misdemeanor from about 25 years ago, does anyone know if it will keep me from getting a work visa in countries such as Austria, Germany, or France?
Each country has different laws, rules, and regulations.
For Germany, then laws such as the residency act, talk about "serious criminal offences". (https://www.gesetze-im-internet.de/englisch_aufenthg/englisch_aufenthg.html#p0989)
If you have been committed of a serious offence involving violence, drugs, or are a member of a terrorist organisation etc. then it is highly likely that you would be denied a work (and residency) visa.
However, for more minor crimes then they tend to be more open. Especially, if a significant period of time has passed since the crime with no other offences having taken place.
They will however judge it on a case-by-case basis, and there is no published list to state exactly what they will and will not allow.
Certainly, I would suggest that when you apply for a visa from your country that you are open and honest. If you try to hide it then this will count against you and decrease your chances significantly.
But that if this was a minor offence and you have kept out of trouble for 25 years, then you would stand a good chance of having a work visa approved in Germany. I have heard of cases where US citizens for examples have been convicted of misdemeanours in the past and received a work permit and are happily living in Germany.