The best practice is to check in your phones software update section and by also using Smartswitch.
If your phone is unbranded i.e supplied by Samsung then they'll send out the update to all eligible phones in a scheduled process.
If your phone was supplied by a network i.e branded then you'd need to speak with your network.
I personally wouldn't recommend using any Custom Roms unless your aware of how to use one and also are aware your phone could end up unstable or in the extreme unusable.
Then Samsung would levy a charge to try and put it right.
Current Phone > Samsung Z Fold³ 5G.
That does not work I even took it to Samsung office and I was ready to pay for them to upgrade it but they refuse ..the only option is flashing with odin and if I brick my phone not even Samsung office will fix ..so I see my sef using the phone like that till I get money to go for a better brand like the oneplus series