This can be a problem, if the sender knows you read the message and will ask questions when message not answered right away. To avoid this problem there are actually a number of tricks that can be done.
There is another way besides turning off the read. Namely, by activating airplane mode (airplane mode) on your cellphone, as quoted from the India Today page, Monday (2/8/2021).
Messages remain marked as unread even when the HP airplane mode is turned off.