Would a sublingual dose be possible/more effective? Research in other (um, yeah, medicinal!) compounds shows that it can be an effective pathway to the bloodstream rather than trying to survive the digestive system.
It would be hilarious if people wound up snorting or boofing their GLP-1s (≧▽≦)
Sublingual is even harder. The sublingual mucosa is thin but selective. It strongly favors molecules that are small, lipophilic and uncharged. Semaglutide is about 8-10x too big, highly polar and charged.
Injection is really the only method with any substantial bioavailability. BUT, low (<1%) bioavailability does not necessarily mean useless.