macOS 10.14 Mojave is the Last version of macOS to support 32 bit anything as in software drivers and applications
So, if you intend to upGrade to say macOS 10.15 Catalina and above
You will require updating or UpGrading all 32 Bit drives and Applications
Good place to start and checking for 32 bit, would be https://www.stclairsoft.com/Go64/
Also, starting in macOS 10.15 Catalina and above
iTunes as we knew it has changed into Separate Applications, TV, Music, Podcasts, Books
Each newer version of macOS places more demands on the computer
Suggestion are to have at least 8 GB for light usages and 16 GB or more of RAM fr more intensive usages
iMac 21.5" from 2017 - Fusion Drive or an all SSD Configuration
Fusion Drives work but may not be a responsive as under High Sierra macOS 10.13
Computer Qualifying for macOS 13 Ventura
Computer Qualify for the Monterey upgrade
macOS Big Sur 11 hardware requirements
macOS Catalina 10.15 hardware requirements
Always make a Time Machine Backup before doing any upDates / upGrades
To truly protect your non replaceable Data - have a 3-2-1 Rescue Plan in place and always current
3 Backups using 2 methods and 1 off site incase of natural disaster or un-natural disaster.
Each of the above should be done to a Dedicated Single Purposed External Drive
Below link is to Augment what TM Backups does
Not to Replace TM BAckups
https://bombich.com