Big Sur slowing down my computer

Download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Additional Text button to include the report in your reply.

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck in the Etrecheck's Privacy preference pane so that it can get additional information from the Console and log files for the report:

Also click and read the About info to further permit full disk access.

Then we can examine the report and see if we can determine what might be causing the problem.

Have to agree with @ Old Toad. Without giving a more complete picture ( via Etrecheck report ) and / or at least an Activity Monitor Screen Shot it will be only guessing. Not too much constructive help can be offered.

If you'll run Etrecheck and post the report maybe we can tell you if there might be some 3rd party software that might interfere with good system performance.

anybody have done it and experienced a slow down ?

No. I've installed it on a 2018 MBP.

It won't cause a slowdown on a 2017 MBA, but what crapware you might have installed could possibly cause it to slow down.

Only you can answer the question whether it will slow your Mac down.

So if no crap ware installed except a program from FileMaker , cause I’m all iCloud drive , it should be good ?

It should run fine.

Given that the only people that come here are complaints, and I don't remember a huge number of posts about 2017 MBAs slowed by Big Sur, I would surmise that the vast majority of 2017 MBA users aren't having a problem.

Try opening Activity Monitor from the Others folder in Launchpad. Click View and enable All processes. Look for any runaway processes to determine what is possibly wrong

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Then the only answer we can give is "yes or no" because we don't have enough information.

Good luck.

Second that.