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AFAIK, it takes less energy for the smartphone to connect to the home-router via Wifi which is only about 10m away than to connect to a 4G cell tower which is about 500m away.

Compared to 4G LTE, 5G NSA takes more energy from the smartphone because of using more carrier aggregation (to attain speeds of 1Gbps or higher) and the need to connect to both LTE Band 28/700MHz and 5G Band 78/3500MHz.

So, if we do not need higher speeds and/or more data, 4G LTE is enough, ie no need 5G.
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Ur sim card and plan subscribed to 5G or no?

Im asking this because i found that even CTO of telco operator also doesn't aware his plan need to subscribe 5G....

this is umobile thread
the new u plan have 5G  access
Previous GX 5G ready but 5G pass have to pay

Is this a Pixel phone?

Generally, overseas imported phones are not allowed to connect to the 5G network here

Software modding is most likely needed, unlock bootloader, root, etc
But that comes with it's problems too like failing safetynet/play integrity and then apps refusing to work due to that

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Fyi, .......

https://www.digital-nasional.com.my/why-sam...s-dnbs-response - Why Samsung and iPhone devices can’t connect to 5G in Malaysia? Here’s DNB’s response - 16 Feb 2022
.... The statement said the availability of 5G devices in Malaysia falls within the purview of the respective device manufacturers.

DNB emphasised that it isn’t their responsibility to certify or approve 5G devices. However, they provide facilities for manufacturers to conduct tests such as initial static tests as well as a test route to conduct on-the-road drive tests so that device manufacturers can configure their devices and update the firmware so that it is compatible with the 5G network.  ...

When we put the Yes 5G SIM in a Samsung Galaxy S21 Ultra, the device could only get 4G. ...

= so, in general, the OEMs won't configure imported or non-locally-sold smartphones/modems for DNB's 5G network, except for imported high-end ones like iPhones and Samsung Galaxy S-series (configured for DNB's 5G thru OTA updates, eg iOS 17.0.3 update).
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Are you able to flash to Malaysia XME firmware ?  If yes you have a chance.
edited :

I just checked, no you won't be able to flash XME firmware, there isn't one  https://samfw.com/firmware/SCG08

Someone else got similar issue. Albeit it's the neighbouring country, Korea.
Got both 4G b28 and 5G b78 bands still no 5G for his S22U.

https://forum.lowyat.net/topic/5426311/+60#