Hi Nuq,
Whilst it is possible to just replace the back glass on the Pixel 8, I would not recommend it, as Google has secured this with very strong adhesive. Further more, It is very easy to damage your wireless charging flex cable, or the coil itself as it is also adhered to the back glass, making removal difficult and risky.
Here is a link to a video and replacement back glass in case you want to attempt this repair
Video: https: //www.youtube.com/watch?v=K6MFHuZ4T-g
Back glass: https://www.ebay.com/itm/155917192178?var=456318135924&hash=item244d638bf2:g:SJYAAOSwSzhlZzMg&amdata=enc%3AAQAIAAAA4FjDbp9oIRC9HwAwLOjKP8QyqVXLZfyahLaG5K9askZoYPCYc5OmURoRUj3S7IdIwX1C1bZCUyNab17rSPe2ImtcLUWbgbWpVWkHcEL9pJnHH%2F1kKol1owD%2BQWuVf51gwmvDkOfc%2BZMaTSfaCbOzX4tqT7250puEyjoWGwd%2FAPFOMaVMMtzeDL5EFVeO9vXzTE3qxmGwv3SPWiHlVy%2BIe8%2B5kB0BUvEPBUvqygDeQDrs0PmNOM4E4cADjrTRsiT%2B1cqRx9RqV%2BjmEPxpD5UGITKvGC0%2FH5%2BxhSDaUc0p4hsB%7Ctkp%3ABk9SR8bL3JKcYw
another option, which whilst not risking your wireless charging functionality is more pricey is to replace the entire housing, back glass included. I will also attach link to a replacement housing however Ifixit unfortunately does not have a guide on performing this repair.
Housing: [product|IF356-399-5]
Whilst the broken back glass has removed your phones water resistance, It wont have any kind of impact on the phones functionality, so a replacement will only benefit the phone cosmetically.
I hope this helped, let me know if you have any other questions : )