How does Approval Voting affect spoiled ballots?

Approval Voting will drastically decrease the number of Spoiled Ballots.
Technically, it’s impossible to spoil an Approval ballot by intentional markings. A candidate race in which anywhere between zero to all of the number of candidates chosen is a valid vote.  Nevada recognizes a vote for all of the possible choices as a vote for none of the above. It does not invalidate the vote or the ballot.
In Colorado, clerk’s and volunteer judges review the ballots during pre-scan handling. Potential errors from food stains and crumples cause staffers to replicate ballots before feeding into their million dollar machines.
Voters have to work hard to make a paper ballot unreadable to the scanning systems. In the French and German Approval Voting studies, under 0.5% of voters managed to cause spoiled ballot errors. (1 error in 200 ballots)
It is very difficult to spoil an electronic ballot. This is generally caused by voter-operator error, and a do-over does not require a ballot re-issue as all errors are resolved before the ballot is cast.
Vote for One candidate selection on Plurality Voting ballots are treated as Spoiled whenever voters marks more than one choice.
The fact that voters do this tells us that they have more to say than Plurality Voting permits. Consequently, in the 2000 U.S. elections, nearly two million ballots were spoiled. Plurality Voting’s spoilage rate is approximately one in fifty, which is about four times more than Approval Voting.
In the 2000 elections half a million of the ballots were spoiled due to more votes than Vote for One Plurality rules permitted.

Colorado’s newest party is seeking citizens of the state to register to vote as Approval Voting Party members.

The Approval Voting Party has been established in Colorado. On October 1st 2019 over one-thousand Colorado voters have registered as AVP which was founded in late 2018.

The second statewide convention will be held in Denver on March 1st 2020.

Voters naturally want to choose more than one.