You can absolutely share! There are “Gondola Sharing” tours where you book just one seat in a boat of 6 people. It’s way cheaper, usually around 30 Euros.
I did this last year and it was great – I met a nice couple from Australia and we all shared the experience. You can find these shared seats via Gondola Rides in Venice https://alle.travel/en/venice/category/gondola
The only downside is you might not get to pick the exact route, but you still see the main sights. It’s a perfect budget-friendly way to do the “classic” Venice experience without breaking the bank as a solo traveler.