Macbook Pro 13" mid 2012 with macOS Catalina slow start up

Go step by step and test.

1. Reset PRAM:  Reset NVRAM or PRAM on your Mac - Apple Support

     Settings that can be stored in NVRAM include sound volume, display resolution, startup-disk selection, time zone, 

     and recent kernel panic information. 

     The settings stored in NVRAM  depend on your Mac and the devices that you're using with your Mac.

2. Reset  SMC:   How to reset the SMC of your Mac - Apple Support   Choose the appropriate method.

    Quote:

    Resetting the system management controller (SMC) can resolve certain issues related to power, battery, fans,

    and other features.

3. Startup in Safe mode. https://support.apple.com/en-gb/HT201262 Choose the appropriate method.

    To leave Safe Mode, choose “Restart” at the bottom.

    Quote:

     Safe mode prevents your Mac from loading certain software when it starts up, including login items, 

     system extensions not required by macOS,

     and fonts not installed by macOS. It  also does a basic check of your startup disk, 

     similar to using First Aid in Disk Utility. 

     And it deletes some system caches, including font caches and the kernel cache, 

     which will be created again automatically as needed.

A hard drive is a common cause of "the slows" in that model. Most 2012 MacBook Pros have mechanical hard drives that make them feel slow.

Most drives in that model were under-specced from Day One, considering the logic board's speed potential. Mech drives can also slow as they age. A ten-minute boot time implies a failing hard drive and/or a serious infection of worthless third-party anti-virus, security, or so-called "cleaning" apps. Those are Mac killers.

There is also a possible slow performance issue with an inexpensive, user-replaceable part—the hard drive cable. It is subject to wear from normal vibration of use and transport. The wear, that can mimoc a failing hard drive, can show up in as few as 3-5 years.

Given those potential issues, for us to see hard data on your computer's current condition we need a snapshot of the systme configuration. Fortunately there is a safe, secure way to do that. 

We can quickly and within the confines of these forums help you determine what issues are at play if you use EtreCheck Pro, available here:

https://etrecheck.com/index

The free version will do nicely for this purpose, although the app is worthy of our financial support.

We can see hard data about drive performance, software issues, and RAM usage. Etrecheck is the development of a long-serving and trusted contributor here expressly for displaying diagnostic information in these forums to help us help you. It will not reveal any personal or secure information. Many issues have been resolve din one post here beacsue and EtreCheck report was included.

The report will be too long to post by copy/paste. To post the entire report here, please follow this instructions in this User Tip:

How to use the Add Text Feature When Post… - Apple Community