Wayan,
Update: Upon further investigation I can create a class in my CSS file as follows:
.invisible {
visibility: hidden;
}
I can then add a <div class="invisible"> to wrap the existing HTML code as follows:
<div class="invisible">
<a href="#" class="back-to-top"><i class="ri-arrow-up-line"></i></a>
</div>
While this in turn serves to make the button invisible on all devices (not what I want), I might then add code in an effort to make the button invisible depending on the device used. This noted, I'm sure we can all agree how redundant and lame this would be as opposed to using the display property (described in my previous post) that for whatever reason I cannot seem to get to work. What say u?

You should add to that code
@media screen and (min-width: 64rem)
.invisible {
visibility: visible !important;
}
//////You can make that 64rem lower or higher, but that width is roundabout where most laptop devices start.//////
which is about where most laptops start)

Wayan,
Finally resolved. I apologize for the additional posts. I feel like I've been going batty and require some sleep as I had the solution staring me right in the face all along. Problem is, I kept looking at my laptop where the button is displayed/visible as intended as opposed to my mobile phone where the button is no longer displayed. The solution was simple in that all I needed to do was add a division with the display property class for bootstrap 4.5 as follows:

<div class="d-none d-sm-block">
<a href="#" class="back-to-top"><i class="ri-arrow-up-line"></i></a>
</div>

Thanks again for your assistance regarding this matter. I believe I am now ready to focus on the SEO aspects of my new website.

That's great, I. Am not a big user or fan of bootstrap so a little bit lacking in code and CSS for it, glad you got it sorted, wishing you all the success for your. New venture.
Should you wish to contact me directly for anything in the future you can always fill out the form on my site
mawarputih.id

Wayan,
Thanks for the offer. I will be sure to check out your site and fill out the form. On another note, as I am also new to bootstrap, while I am satisfied to date in using it for my new one-page website, I must admit that I had to jump through a lot of hoops in modifying and getting the contact email form part to work as intended in which event the technical support provided was essentially useless. As such, I would be most interested to learn why you're not a fan of bootstrap as your reasons may prove beneficial for me down the road.

Wayan,

FYI, I recently visited your site and couldn't help but notice some technical issues I wanted to bring to your attention in confidence rather than post this information to the forum. If interested, you can let me know by sending a private email to info@seoauditspecialists.com. Moreover, as I need to build a portfolio in SEO, if you like, I would be willing to instruct you on how to address some of the issues I found on your site (pertaining to technical SEO) pro bono.

Thanks but as it is only temporary mostly for contacting me on the form, I have placed one of those robot thingies, for noindex,nofollow, noindeximage as I don't want it to appear on SERPs

but if you have spotted something that isn't working them please let me know

Thanks again

Wayan,
Understood if you do not want this page to appear in the SERPs. The other issue I noticed was the overlapping text (see image file attachment) on your home page as I didn't know if you were aware of this or not. The only other thing I noticed right off the bat is that the page was shown as being unsecure in my browser address bar that in itself can discourage people from clicking on the link if and when it should appear in the SERPs. In no disrespect, if it wasn't for the fact that I had already corresponded with you on the forum, knowing what I know now, I would have never entered the URL you provided in my address bar to begin with.

Hi
Yes thanks for that, it appears I forgot to remove some text that I decided I didn't need,
Sorted that out now thank you

HTTPS I'm not sure about , I have it with my hosting service, but something went awrylast week with them I will check it out

Thanks again

OK fixed that as well
Thanks again for pointing it out