1. Find unused
Find the unused Fields. "Where is this used?" in Setup, and a search across all Metadata in VS Code or/and use an AI tool if you like. Check the data too, zero references plus an empty Field is your candidate.
2. Remove Access
Then remove Read access from the Profiles and Permission Sets and wait a cycle. Add again as soon as anyone complains.
3. Delete Field
And then delete them. Make sure you backup any data.
Happy deleting
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