I feel like the tablet is hindering my sons speech...

first step is setting limits. it's probably gonna suck. he's gonna probably act out and throw tantrums, but you gotta hold the line.
to engage with him more, i'd say involve him. whatever you're doing -- dishes, laundry, cleaning, book reading, coloring (am i the only one who loves coloring books?). just involve him

the trick is to replace the tablet/tv, not just get rid of them (vould also try watching things on tv together and talking about -- more boring things that aren't going to hold his attention 100%)

I'd like to preface this with every child with autism is different ✨️

My son is currently 8 and has autism as well. When he was a lot younger, this was also a concern for my husband and I. After speaking with his therapist, and learning more about the way he processes language (he's a gestalt processor), this helped us a lot more to understand how the tablet was actually helping him in a way.
He would watch a lot of shows where the characters really didn't talk, it was more more narrator based.. but we'd noticed that he would narrator on his own or describe what he saw. We were shocked in the best way possible! Now, he has a ton of scripts/phrases that he uses and his language is a lot more intentional. This is still communication that is hard to understand, but we're currently in the process of getting an AAC tablet, that will help bridge the communication even more. This can be gotten though your insurance, if its something you'd like to look into.

I also agree with setting limits. We used to set a timer, and gave him reminders, "10 more minutes and the tablet has to get some sleep" etc. He's gotten used to the routine, so we no longer need timers.
I also know the feeling of him only wanting to play with day. My son has toys and games that are dad specific, and love that for them. It took a minute, but I got there lol.
You definitely got this mama ✨️

Get some outdoor toys. You can spend whole afternoons just drawing with chalk outside. Draw hopscotch, a city, a flower garden, some animals, your chalk outlines then color them in. Draw all the different car logos and have him point them out when he sees them on cars. Blow some bubbles. My kids ❤️LOVE❤️ toss and catch. Some kids love costumes, some love hide and seek, some want to be pushed on a swing, some just want you to read them a book. Tablets are no match for parental attention, so give him your eyeballs and see what he wants to do with you! If you're really drawing a blank, ask dad for some ideas. He seems dialed in and can probably get you going in the right direction. Toss the tablet, you've got this!

Have you got any ideas of how to engage him in his world? What does he like to do? BBC parenting website has some ideas.

If you think the tablet is bad for him get rid of it