[Samsung Galaxy S21 Ultra] dr.ketan:
Here some my thoughts and explanation about TWRP backup and restore

Firstly brief explanation about what does partition contains.

Boot : It is Kernel

Recovery : It is Recovery

super : That contains odm,product,system and vendor partitoin all togather.

optics : CSC files (where we routinely making changes for csc features) and network settings depending on your carrier

prism : carrier related apps and other stuff . In odin when you flash CSC*_ or Home_CSC* these two optics and prism gets flashed.

data : That is all your installed app and made changes in settings

Now what to backup/restore?

boot - Helps if something messed up with magisk or waht to restore kernel after flashing custom.

recovery - usually it doesn't require but if you flash some other recovery(TWRP) and you want to restore one in backup, that helps

super : As stated above these is main system, if something you have messed up in system/vendor (usually with flashing something, or erasing something) you can restore by super.img.

optics and prism : as explained above are CSC files, Rather than restoring it, I prefer to flash HOME_CSC*.tar.md5 to make csc compartment clean. So to backup or not not much important.

data : This very sensible part. I prefer to make data backup when there is no samsung a/c or Lockscreen protection there. Also don't restore it cross version of ROM. Also some common mistakes user making is, He/She clen install ROM and then restore data partiton of previous ROM. This is worst then even dirty installing ROM, never do it. It is just false sense of satisfaction that you made a clean install. According me, data partiton backup best to be made just after complete clean install ROM and setting up device without adding any account and lockscreen protection. So when you restore this backup, you will have a device just like you recently completed clean install and save your time to setup initial wizard

Backup Application,Call logs,Contacts,SMS etc

Titanium backup was ruling for decade for these but since A11 it's not trust worthy and on A12 almost useless.

Swift Backup is now my choice (Some other like Migrate, App dash (by RD XDA dev flar2) also alternatives)

For contacts : I do prefer google sync. Just adding google ac everything will be restore on it's own, provided you are saving contacts in google. In case you want to make off line backup of contact, there is a built in utility in phone. Contact - settings - export - This will create a file. Similarly browse same file while you want to import contacts. Catch in this is your contact image will not retain size and it just backup thumbnail picture.

Only one utilility I have found that makes offline contact backup without distoring image quality is My Phone Explore client (needs on both PC and Phone). Also this utility is best for wireless file manager.

Schheduled backup - A must needed utility.

I always prefer clean installation (Factory reset withot wiping media files) and really it takes less than 30 minutes to setup everything.

If you enable schedule backup utility in your Backup app (e.g Swift backup have this) and make some profile like

1.Backup - new app at X time then it will auto backup all app that you have new installed at given time

2.Backup updated app at x time - This will make backup of any app that you have updated in store will backup at given time

3.Any app which get data changes frequently and you needs data changes like whatsapp then create a profile favorite app - add whatsapp in favorite and schedule it to make backup daily at given time.

with these your device always remain ready to clean install anytime instead of last moment backup or some urgent clean install needed.

Also Folder Sync is good utility if you needs duplicate copy of files from Internal storage with scheduled operation.

Hope this may helpful and answer lots of queries for many.