Is there a way I can buy a module on Beyond but implement the module on roll20? I am asking as we play on Roll20 but we create and maintain our characters on DNDbeyond. The Module in question has some starting Careers that I would like the group to be able to access on DND Beyond? Second question can a player share content in a campaign? Say the DM who created it has Tashas but not Glory of the Giants and the group would love to access feats etc from that book in that campaign.

There is no overlap between purchases on the two sites, if you're maintaining your characters here I'd say buy it here and then manually add in whatever you need in Roll20, as that's easy to do.

Everyone's content is shared in a campaign with content sharing on. It doesn't matter who turns it on, once any person who's in a campaign turns it on, content owned (on this site) by anyone who has a character in that campaign will be shared with all other characters in the campaign.

Not that easy to copy everything over but understood.

You can use the Beyond20 browser extension.

Make character on D&D Beyond, click on D&D Beyond and the roll happens on Roll20.

This is what we do. But our adventure content is mainly in roll20

Well, no. No extension can carry over all content from one to the other.

Have you tried AboveVTT instead of Roll20? It's a browser-based VTT you can run from D&D Beyond - so it works for all D&D Beyond content.

If this is still not what you're after then I have no idea at all what you want.