How I do that?
I researched several things over years for this purpose.
- Bookari/Mantano - Android and iOS app (no Web, no Desktop, works reliable with Samsung DeX Pad which means it could be used on big screen). Sign-in required for sync. Paid cloud subscription required. Can be slow on large libraries (6k+ books/12k notes, even while I paid subscription for that level of library). Bookari 4 uses Adobe's renderers for epub2 and epub3(and you can choose renderer) (this means that if you provide them file which will crash app in some situations or just being rendered incorrectly, they can do exactly nothing about it. This was confirmed by support several times). Epub3 renderer have...issues. Bookfusion one is better in my opinion.
- Moon+ Pro - Android app only (no Web, no Desktop, works reliable with Samsung DeX Pad which means it could be used on big screen). Sign-in required for sync but it's sign to your own Dropbox/Google Drive account. Embeds notes directly in PDFs (Bookari and (apparently) Bookfusion doesn't do that). Strange sync logic (it looks like it assumes you start book on one device and continue SAME on another). As far as I understood, they use their own epub renderer and licensed PDF renderer.
- Bookfusion -

. Everything skillachie said is true. Android/iOS clients. Web client. Calibre plugin for uploading (you can also upload via Web (as far as I understood, you can also upload from mobile app but I never used this). Paid subscription is required for anything serious if you need sync. Doesn't appear to slowdown with big library. Dictionary integration: Moon+ does this better, even Bookari does this better. Issues with GUI (I asked directly about most problematic of them and got answers like 'this will be fixed in 2019'). If some file renders incorrectly, this can be fixed by sending it to support. Sometimes it's rather fast.