grammar - Is it "Most of the reading was done" or "Most of the reading were done"?

I wrote a blog post, which has the below sentence.

I owned a few paperback books, but most of the reading was done on my
15.6-inch laptop screen.

Grammarly extension pointed out an error with this statement.

It told me to replace was with were. It gave me the following explanation.

The singular verb was does not appear to agree with the plural subject most. Consider changing the verb form for subject-verb

agreement.

I somehow feel was is the right word here, but don't know why.

I need your help folks. Can you please tell me which is right and why?

Thanks!

Answer

Most of something noncountable or continuous is singular: most of the house is carpeted; most of the summer is hot; most of the milk is bad; most of the public is undecided (US English).

But most of the items that are countable are plural: most of the rooms in the house are carpeted; most summer days are hot; most of the cartons have spoiled; most of the public are undecided (UK English).