SQL Server 2019

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create table junk(col1 char(1));
insert into junk values('a');
insert into junk values('b');
insert into junk values('c');
3 rows affected

SET SHOWPLAN_TEXT ON;
select * from junk where col1='a' or col1='b';

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select * from junk where col1='a' or col1='b';

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  |--Table Scan(OBJECT:([fiddle_9679c14d4827458988804630bf9a4b01].[dbo].[junk]), WHERE:([fiddle_9679c14d4827458988804630bf9a4b01].[dbo].[junk].[col1]='a' OR [fiddle_9679c14d4827458988804630bf9a4b01].[dbo].[junk].[col1]='b'))

select * from junk where col1 in ('a','b');

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select * from junk where col1 in ('a','b');

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  |--Table Scan(OBJECT:([fiddle_9679c14d4827458988804630bf9a4b01].[dbo].[junk]), WHERE:([fiddle_9679c14d4827458988804630bf9a4b01].[dbo].[junk].[col1]='a' OR [fiddle_9679c14d4827458988804630bf9a4b01].[dbo].[junk].[col1]='b'))