Can I sayy,

(a) John enjoys to collect stamps.

'Enjoy' goes with gerunds; 'John enjoys collecting [not to collect] stamps'. Below is a partial list of verbs that go with gerunds only.

"admit, appreciate, avoid, deny, discuss, enjoy, escape, finish, imagine, miss, postpone, practice, quit, recall, resist, risk, suggest, tolerate." - Diana Hacker.

Best wishes,
Hoa Thai
Vincent TeoCan I sayy,

(a) John enjoys to collect stamps.

John enjoys collecting stamps.
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 Hoa Thai's reply was promoted to an answer.
Thanks! I learn it by heart!!