A newspaper report from 2024-02-21 says:
Minnesota Dems offer modest gun control agenda, fearing election backlash • Minnesota Reformer
Some progressive DFL lawmakers are aiming for laws restricting the sale and possession of semi-automatic rifles like the AR-15,
but slim majorities in both chambers and skittish caucus moderates will make passage difficult
— especially in an election year when all 134 House seats are on the ballot and the issue could create political headaches for swing-district Democrats.
…
proposing a bill this session that would ban the possession of large-capacity magazines, semi-automatic “military-style assault weapons” and .50-caliber or larger guns.
…
Last week, the Reformer asked Walz during a media availability whether he supports a semi-automatic rifle ban.
The governor said he would need to look at the bill language.
“The one thing I can tell you with absolute certainty is we do not need these weapons of war in our classrooms, on our streets, in the Capitol building,” Walz said.
“I’m interested to see what comes up.”
The key point is that they are talking about assault rifles: "rifles like the AR-15", "weapons of war", and about large-capacity magazines (e.g. hundreds of rounds).
So no, whatever he may have supported, it wasn't banning semi-automatic rifles in general.
No politician that wants to be reelected would support such a ban, given that 500,000 hunting licences are issued each year in Minnesota (population 5 million), and each of those hunters has family and friends that would agree that such a ban would be ridiculous.
Canada, where I live, has very strict gun laws, but the only restriction on semi-automatic rifles is on their magazine capacity (if you can't hit the deer in 5 shots, you have lots of time to reload before the next one comes along).
There is no significant support for banning the rifles here.
And his politician's response, "need to look at the bill language", indicates that he was not a supporter.
bans on semi-automatic rifles
is implied to mean banning all semi-automatic rifles, but is worded so that it could be some degree of true for gun control measures that target magazine capacity or aftermarket modifications to firing rate or whatever