Todoist seems to be the best tool to fit your needs. I know this may not meet one of your specifications (It's only available for MacOS) but Things app has been great to me. The next best thing is TickTick. It has a webapp, so basically it is. Notion is also a great tool but a tad "hammer on a baby toy" for a simple To-do app replacement, IMO. But it also has a webapp.
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Todoist seems to be the best tool to fit your needs. I know this may not meet one of your specifications (It's only available for MacOS) but Things app has been great to me. The next best thing is TickTick. It has a webapp, so basically it is. Notion is also a great tool but a tad "hammer on a baby toy" for a simple To-do app replacement, IMO. But it also has a webapp.