In "Arthur's First Day," an upcoming special scheduled to premiere on PBS on September 6, the bespectacled aardvark and his pals befriend some new classmates -- including a Sikh boy named Samir.
Greg Bailey told me that the show was essentially renewed on a season-to-season basis, by the end of whatever current season they were producing, they didn't always know if they would be renewed or not, hence why a number of more recent seasons conclude with an episode that could be considered to be series fauxnales, not just "The Last Day" but also "The Best Day Ever."(And again, you can tell "The Last Day" was intended to be a possible series finale, but PBS ended up ordering more episodes.)
It probably depends on your station but the 24/7 PBS Kids channel in my area frequently airs reruns of the old seasons.I also wouldn't be surprised if the older episodes are also rarely seen nowadays due to not being HD-compatible. Though I did learn in this thread a while ago, during the midst of the COVID-19 crisis, that some of the oldest episodes did resurface on PBS at some point.