https://www.statscrew.com/minorbaseball/t-wg15427
1999 Winnipeg Goldeyes Northern League Central 48 38 Roster Stats 248,488 6,061
2000 Winnipeg Goldeyes Northern League Central 48 37 Roster Stats 271,513 6,465
2001 Winnipeg Goldeyes Northern League Central 52 38 Roster Stats 292,095 6,491
2002 Winnipeg Goldeyes Northern League Central 56 33 Roster Stats 303,786 6,200
2003 Winnipeg Goldeyes Northern League 55 34 Roster Stats 300,760 7,161
2004 Winnipeg Goldeyes Northern League 56 39 Roster Stats 323,241 7,027
2005 Winnipeg Goldeyes Northern League 47 48 Roster Stats 322,758 6,867
2006 Winnipeg Goldeyes Northern League 52 44 Roster Stats 312,213 6,504
2007 Winnipeg Goldeyes Northern League 52 43 Roster Stats 300,938 6,542
2008 Winnipeg Goldeyes Northern League 51 45 Roster Stats 284,398 6,464
2009 Winnipeg Goldeyes Northern League 55 41 Roster Stats 278,099 6,180
2010 Winnipeg Goldeyes Northern League 46 53 Roster Stats 271,399 5,654
2011 Winnipeg Goldeyes American Association 60 40 Roster Stats 275,521 5,740
2012 Winnipeg Goldeyes American Association 55 45 Roster Stats 285,263 5,705
2013 Winnipeg Goldeyes American Association 56 44 Roster Stats 276,359 5,880
2014 Winnipeg Goldeyes American Association 63 37 Roster Stats 258,429 5,618
2015 Winnipeg Goldeyes American Association 47 52 Roster Stats 258,922 5,284
2016 Winnipeg Goldeyes American Association 58 42 Roster Stats 231,206 4,817
2017 Winnipeg Goldeyes American Association 62 38 Roster Stats 219,556 4,391
2018 Winnipeg Goldeyes American Association 41 59 Roster Stats 219,370 4,477
2019 Winnipeg Goldeyes American Association 57 43 Roster Stats 195,787 4,079
As you can see from the stats above, The Goldeyes basically sold out or had near sellouts for the first 5 years at the new stadium...they expanded the stadium in 2003 to accommodate an additional 1200 seats. The following five seasons they averaged over 6,000 per game.
Starting in 2010 (1 year before the Jets came back) the average dipped to mid-5000s and stayed that way until 2015, so I don't think it's fair to say the Jets had any impact on Goldeyes attendance - it was essentially the same for 5 or 6 seasons. Then in a matter of 4 seasons average attendance dropped from 5600 to 4300. 2 seasons later in 2019, it dropped further to 4,000. Last year, the average was 3400. So far this season the Goldeyes are drawing 3100 per game.
The jets didn't effect attendance so it's something else. My bet would be boomers and the previous generation dying out or being too old to attend games. They are not being replaced by younger people looking for a night of "cheap entertainment." That and the decline in the quality of baseball compared to 20 years ago (more competition from better independent leagues) and less attractive pricepoints for tickets which used to be $10 or cheaper not that long ago.
I also think all those allegations against the former mayor plays a role in declining attendance. Who wants to put money into the pockets of a person who may have stolen hundreds of thousands (or more?) dollars from taxpayers?